Content

Chapter 1 Illustration Instruction ...................................................................................................3

I. Definition of Main Harness Inserters ....................................................................................3
II. Definition of Body Earth Points...........................................................................................7
1. Earth Definition ............................................................................................................7
2. Distribution of Various Earth Points and Main Modules ..............................................7
3. Photos of Earth Points...................................................................................................8
III. Instruction of Main Circuit Symbols ..................................................................................9
IV. Auxiliary Instruction of Circuit Diagram ..........................................................................10
1. Instruction of Power Supply and Earth Wire ..............................................................10
2. Wire Size and Color ....................................................................................................10
3. Definition of Main Controls........................................................................................10
4. Pin Definition Explanation..........................................................................................10
V. Fuse Definition ................................................................................................................... 11
1. Fuse Number............................................................................................................... 11
2. Fuse Position and Function Instruction.......................................................................12
2.1. Front Compartment Relay Box Fuse................................................................12
2.2. Instrument Relay Box Fuse..............................................................................13
Chapter 2 Circuit Control Theory Diagram .................................................................................14
I. Starter Charging System ......................................................................................................14
II. ABS Control System ..........................................................................................................15
III. Airbag ...............................................................................................................................16
IV. Backup Radar ....................................................................................................................17
V. Electric Rear View Mirror ..................................................................................................18
VI. Engine Anti-Deterrent.......................................................................................................19
VII. A/C, Defroster System.....................................................................................................20
VIII. Ceiling Lamp, Luggage Boot Lamp, and Sunroof System ............................................21
IX. Front/Rear Wiper System .................................................................................................22
X. Turn Signal Lamp System..................................................................................................23
XI. Radio/Player, Horn, Cigarette Lighter ..............................................................................24
XII. Headlamp, Fog Lamp System .........................................................................................25
XIII. BCM System..................................................................................................................26
XIV. Instrument System..........................................................................................................27
XV. 473 Engine and Electric Injection System .......................................................................28
 Chapter 1 Illustration Instruction

I. Definition of Main Harness Inserters

Engine/ECU (inserter of engine harness and ECU harness)

ECU/front (plug of ECU and front compartment harness)

8 7 6 5 4 3 2

16 15 14 13 12 11 10 9

ECU/instrument (plug of ECU and instrument harness)

1 2 3 4 5 6 7

8 9 10 11 12 13 14

I n t e r i o r /i n s t r u m e n t A ( p lu g A o f i n te r i o r h a r n e s s a n d
in stru m e n t h a rn e ss )

13 12 11 10 9 8 7 6 5 4 3 2 1

26 25 24 23 22 21 20 19 18 17 16 15 14

Interior/instrumentB（plug B of interior
harness and instrument harness）

2 1
4 3
 Interior/front (plug of interior harness
and front compartment harness)

8 7 6 5 4 3 2 1

16 15 14 13 12 11 10 9

Instrument/engine A (plug A of
instrument harness and engine)

7 6 5 4 3 2 1

14 13 12 11 10 9 8

Instrument/engine B (plug B of
instrument harness and engine)

Instrument/front A (plug A of instrument

harness and front compartment harness)

1 2 4 5 6 7 8 9 10 11 12

18 19 22 23 24 25 26

Instrument/front B (plug B of instrument

harness and front compartment harness)

2 1
4 3
 ECU pin definition

pin definition

1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16

1 2 4 5 6 7 8 9 10 11 12 13
14 15 16 17 18 19 20 21 2223 24 2526

COMBINED INSTRUMENTS

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17
 Interior/left front B (plug B of interior harness
and left front door harness)
Interior/left front A (plug A of
interior harness and left front door 1 2
harness)
3 45 6 7 8
12 34
9 10 12 13 14
5 6 7 8 910

Interior/left rear（ plug of

interior harness and left rear
door harness）
Interior/right front A （ plug A of interior
harness and right front door harness
1 2 3 4
1 2
34 5 6 7 9 10

Interior/right rear（plug of
interior harness and right Interior/right front B （ plu g B of interior harness
rear door harness） and right fro nt door harness ）

1 2 3 4 1 2 3 4
5 6 7 8 9 10
5 6 7 9 10

Interior/ceiling lamp (plug of

Interior/airbag (plug of
interior harness and ceiling interior harness and airbag
lamp harness) harness)

1 2 1 2 3
3 4 5 6 5 6

Interior/rear bumper (plug of interior

harness and rear bumper harness)

2 1
6 54 3
 II. Definition of Body Earth Points

1. Earth Definition

G100: Body earth, ABS earth

G101: Left front compartment earth (radiator fan, low beam, high beam, position lamp, turn signal
lamp, front fog lamp, wiper, brake liquid level, anti-deterrent horn)
G102: Right front compartment earth (high beam, low beam, position lamp, turn signal lamp, side
turn signal lamp, front fog lamp, horn)
G200: Power train, fuel position sensor, left front door, left rear door, front ceiling lamp
G201: Electric sunroof
G202: Tail lamp, backup radar, oil pump, rear wiper motor
G203: Luggage boot door (rear wiper, high mount brake lamp)
G204: Tail lamp earth
G206: BCM, seat belt switch
G207: Cigarette lighter, fan, instrument electric box
G208: Audio equipment, combined instrument, various control switches, diagnosis socket
G209: Engine ECU earth
G210: Engine ECU earth

2. Distribution of Various Earth Points and Main Modules

BCM is located
under the driver’s
Front compartment seat
Instrument electric box
electric box
Engine ECU The backup radar module is
Diagnosis socket located within the left guard
plate of luggage boot.
3. Photos of Earth Points
G100
G100(Below battery)
G100

G209, 210(Left lower side of front wall) G101 (at left front longitudinal beam)

G102 (at right front longitudinal beam) G201(At right front ceiling armrest)

G207, 208(at secondary instrument panel) G202 (left rear side of luggage boot)
G204 (below right pillar C) G206 (near BCM)

G200 (below left pillar B)

III. Instruction of Main Circuit Symbols

Symbol Meaning Symbol Meaning

Wiring joint Motor

Fuse position and

Bulb
specification

Relay Switch control

Shield wire Resistance unit

Shield wire Electromagnetic coil

This part is not

covered within this LBD
system

Connector Earth

Note: Please validate specifically the real articles with the circuits for other symbols.
IV. Auxiliary Instruction of Circuit Diagram

1. Instruction of Power Supply and Earth Wire

30: Primary live wire from the battery

30a: Primary live wire from the battery
15: From the ignition switch (IGN1)
15a: From the ignition switch (IGN2)
Ka: From ignition switch (ACC, disconnect at start)
58b(RHEO): power supply for noctilucence illumination
30–(GROUND): Earth wire, from cathode terminal of the battery

2. Wire Size and Color

Secondary color
Primary color
Lead wire size(mm)

3. Definition of Main Controls

This circuit control theory diagram uses “instrument plug/” to indicate the integrated relay plug of
the instrument electric box.
This circuit control theory diagram uses “ECU” to indicate the engine control unit.
This circuit control theory diagram uses “BCM” to indicate the body control module.

4. Pin Definition Explanation

The pin definition explanation of the circuit theory diagram:

For instance as follows:
4.1.
“Instrument/interior/A/6” indicates the #6 pin of plug A of instrument harness and interior harness
connectors;
4.2. “To anti-deterrent module A5” indicates “to #5 pin of plug A of anti-deterrent module”;
4.3. “To ECU25” indicates “to #25 pin of ECU";

V. Fuse Definition

1. Fuse Number

The fuse number within the front compartment relay box is expressed by “EF+number” and
“SF+number”.
The fuse number within the instrument relay box is expressed by “F+number”.
2. Fuse Position and Function Instruction

2.1. Front Compartment Relay Box Fuse

Front Fog Lamp Relay

High Beam Relay

Fan High Speed Relay

Low Beam Relay

Main relay
Fan Low Speed Relay

Electric Fuel Pump

The front compartment relay box is located near the front compartment battery, with the detailed
function instructions of the fuses are as follows:

Fuse No. Capacity Function Fuse No. Capacity Function

SF1 30A Fan, high speed EF6 10A Compressor
SF2 30A BCM EF7 15A Oxygen sensor
SF3 30A A/C EF8 Vacant Vacant
SF4 40A Instrument electric EF9 15A Ignition coil
box
SF5 30A ABS EF10 10A Backup lamp
SF6 30A ABS EF11 10A Right position lamp
EF1 20A Fan, low speed EF12 10A Left position lamp
EF2 15A Front fog lamp EF13 10A Right high beam
EF3 10A ECU EF14 10A Left high beam
EF4 15A Fuel pump EF15 10A Right low beam
EF5 30A Primary relay EF16 10A Left low beam
2.2. Instrument Relay Box Fuse

Diagnosis Access

Blower Relay

Steering relay

Integrated relay plug

Front wiper relay

The instrument relay box is located within the left cover plate of the dashboard, with the detailed
function instructions of the fuses are as follows:

No Specification
Functions No Specification
Functions
 Chapter 2 Circuit Control Theory Diagram

I. Starter Charging System

circuit diagram

Instrument/front B2
Instrument/front B3

Instrument/front
B1
REVERSE LAMPS

Vehicle speed sensor

To instrument charging indicator

Ignition Switch

Instrument/engine B1

/ engine

Interior/instrument
To

Motor

Starter
Battery Battery
body transmission
earth earth
Body Body
earth earth
 Instrument 14#
Diagnosis Access7#

Instrument/front 11
Instrument/front Instrument/front 10
Instrument/front 9
Instrument/front
Instrument/front8
Instrument/engine

Instrument/front
II. ABS Control System

Interior/instrument
High-mount brake light
Brake lamp Switch
Right Brake Lamp

Instrument/engine
30a

15a

30-
Ka
30

15
Left Brake Lamp
 III. Airbag
30
30a
15
15a
Ka

Left side Right side

sensor sensor
PAB switch

Airbag indicator lamp PAB indicator lamp Diagnosis Access7#

Instrument/airbag
plug

Air Bag

Driver airbag Driver side Passenger side

Driver seat Passenger seat
Passenger airbagairbag airbag belt switch belt switch

Special earth
point of
30（-） airbag
IV. Backup Radar

circuit diagram

backup radar

30
30a
15
15a
Ka

Display

Engine/ECU26

Backup radar control

To gear switch
module

Engine/ECU27

ECU/Front 4

Interior/front 2

Probe Probe

30-
V. Electric Rear View Mirror

30
30a
15
15a
Ka
58

Interior/left front

Electric rearview mirrors

Interior/left front Interior/left

front

Interior/left front
Interior/right
front
Interior/right
Interior/right front
front
Right rearview mirror
Left rearview mirror
VI. Engine Anti-Deterrent

30
30a
15
15a
Ka

Anti-deterrent
module

Instrument/engine
Instrument/engine

Diagnosis
Access

30-
 VII. A/C, Defroster System
30
30a
15
15a
Ka
58

A/C switch
Rear windshield defrost switch

Instrument/front
B4

Air conditioner
relay

A/C switch
Instrument
plug9#
Interior
circulation switch
Rear windshield defrost switch

Instrument/front
Blower

Instrument
motor
Interior/exterior circulation

plug 10#

高
High/lo
w 低
Interior/instrument 压
pressure
Fan regulator swithc
Instrument resistor 开
plug1# 关

Interior/luggage
boot door 2
Blower
Defro ster heating coil

Relay ECU/Front 11

ECU/Front 3

Blower switch

30-
VIII. Ceiling Lamp, Luggage Boot Lamp, and Sunroof System

30
30a
15
15a
Ka

Interior/instrument

Interior/instrument
Interior/instrument
Front
ceiling
lamp Ceiling lamp switch

Interior/luggage
boot door4
Luggage boot contact switch

Automatic off

Sunroof

To instrument
1#

Interior/instrument
Door contact switch

Door contact switch

Door contact switch

Door contact switch

Speed signal

Self Self Self Self

earth earth earth earth
30-
IX. Front/Rear Wiper System

30
30a
15
15a
Ka

Wiper combined switch

Terminal number
Front washer
Front/rear wiper washer switch

Rear washer

Interior/instrument

Instrument/front Interior/instrument
Instrument/front

Interior/luggage
Wiper Relay

boot door5
/
Instrument/front
Interior/luggage
boot door
Instrument/front
室/仪
Rear Front
washer washer
motor motor

Rear Wiper
Front wiper motor Motor
X. Turn Signal Lamp System
30
30a
15
15a
Ka
58

To running relay

To BCM24

Alarm
switch

Flash
relay

Turning
Switch
Interior/instrument16
Instrument 24 Interior/instrument15
Instrument22

Left Left Right Right

turn rear turn rear
lamp turn lamp turn
lamp lamp

30-
XI. Radio/Player, Horn, Cigarette Lighter

To antenna

To rear
fog lamp

仪/前

Instrument/engine
Instrument/engine Instrument/engine Instrument/engine Instrument/engine Instrument/engine

Instrument/engine Instrument/engine

Interior/right
Interior/left Interior/left Interior/right
front
front front front
XII. Headlamp, Fog Lamp System

30
30a
15
15a
Ka
58

To instrument 11#
Turn signal lamp relay

Turn light
Turn light

Instrument Instrument
25# Instrument/engine
plug /11 To
Lam p ceiling
control lamp
sw itch Off G re en Fog
Clearance
lamp
lam p
Switch
H ead lamp

Clearance Fro nt
lamp fog Rear
lamp Fog
relay Lamp
control
N octilucence
adjustment switch
Instrument 32#
Instrument/front
B eam selector Instrument 28#
Instrum ent/front
Instrum ent/front
Instrument/front
Front
Fog
Lam p
Low High Relay
Beam To
Beam
Relay Relay instrument
6#

Instrum ent/front
Instrument/front Instrument/front

Interior/instrument

Left

right front fog lamp

left tail lamp

left front fog lamp

rear

right rear tail lamp

fog
右 lam p
Left
示
clearance
lamp 宽
Left
headlam p Right 右 灯
大 License
headlamp Plate
灯
Lamp

30-
XIII. BCM System

Interior/le ft fro nt Interior/right

front Interior/left Interior/left front
Interior/le ft front
Interior/right
rear 6
L eft Front W indow rear 6
（ ） S w itch
B rake right front left rear right rear
lam p w indow w indow w indow
Sw itch sw itch sw itch sw itch To alarm lam p sw itch
A ir
conditioner
relay
A nti-deterrent D iagnose

Interior/instrument
m odule 7#
Instrum ent/front

Interior/instrument9
antenna 14

I nterio r/rig h t Interior/left rear Interio r/ right rear

In te rio r/left fro n t fro n t Interior/instrum ent
In ter io r/left fro nt 6 26
Interior/left Interior/left Interior/left
front front front

H igh potential lock H igh p otential unlock

Interior/front
Interior/left rear

In terio r/in stru m en t Interior/right

com partm ent 5 In terio r/le ft fro n t front Interio r/ right rear
Interior/left
fro nt Interior/left Interior/right Interior/ rig ht rear
fro nt front Interior/left rear In strum en t/in terio r
Left R ight

Ceiling lamp control

A irbag Interior/left
Interior/instrument

signal rear turn turn In te rio r/fro n t1 In terio r/lu g g ag e b o o t

signal signal do o r3

Luggage boot door contact switch

lam p lam p

Four-door contact switch

Speed signal
Starter
Theft-deterrent indicator lamp

Engine hood switch

right rear door lock
right front door lock

left rear door lock

Left
front
d oor
lock

L eft front rig ht front left rear w indow right rear

w indow m otorw indow m otorm otor w ind ow m otor
 To right turn signal lamp

To Left turn signal lamp

To headlamp
switch
switch

Lamp
lamp

Rear
Fog
rear
fog
To

switch
lamp

Lamp
front

Front
fog

Fog
To
Handbrake

lamp
Left
turn
switch

Right

lamp
turn

Headlamp
Parking
lamp

Instrument system
sensor
level
fuel
To

Fuel consumption
Interior/instrument
To

Instrument/engine
To

Interior/instrument
Vehicle speed
signal output
Sensor
Speed

Instrument/engine
To

Vehicle speed
Instrument/engine Fuel warning light Brake liquid alarm switch
To

Engine speed
Instrument/engine
Coolant warning light
To

Coolant temperature

Instrument/front
Brake warning light
Instrument/engine Engine oil pressure alarm lamp
发/
To

Instrument/engine Engine self examination lamp

generator
To

Instrument/engine Power supply indicator light

Seat belt warning light

照
明
灯
Interior/instrument
four-door
contact
switch
To

Interior/instrument Door indicator lamp

airbag
Position

switch

temperature
To
lamp

AIR BAG WARNING LIGHT

coolant

sensor
To

Coolant alarm lamp

Instrument/front

Interior/instrument A10
Position light
ABS WARNING LIGHT
Passenger side airbag alarm lamp
To airbag

Diagnose

Diagnosis Access
To airbag

Instrument/engine
To
XIV. Instrument System

To
 To theft-deterrent

To theft-deterrent

Engine speed sensor

/仪
engine/

/仪
engine/

Accelerator
TOECU36
engine/

Electronic Throttle Valve

KNOCK SENSOR
engine/

engine/
engine/

engine
To ECU42
CARBON CANISTER engine/
SOLENOID VALVE
engine/

engine/
engine/
engine/

engine/

Evaporator temperature
/仪

sensor
To camshaft position sensor
Injector 3
/仪9

Coolant Temperature Sensor

engine/

Injector 4
engine/
engine/

Injector 3
Intake temperature pressure
sensor
Injector 1
engine/

engine/

33 TO
engine/
engine/
前
氧
传
感
器
10

engine/
engine/
engine/

/front 14

Phase sensor
engine/
engine/

10 To engin/
Rear oxygen sensor
engine/

engine/

engine/
engine/
engine/

Clutch switch
发/

TO EF10
/front 2
engine/

Power steering switch

Vehicle speed
sensor
engine/
Ignition Coil

engine/
发/

COMBINED INSTRUMENTS
/Instrument
/Instrument
发/

/Instrument
/front

/Instrument

Brake Lamp Switch

到EF9
/front

/Instrument
/Instrument
/前9

/Instrument 10
/Instrument To lamp control switch
/front

Instrument
/front 10
/front 5

/front 7
XV. 473 Engine and Liandian Electric Injection System

Interior/instrument7
/front

/仪12
Electric Fuel Pump

/前15
Compressor
Air conditioner relay

/front11
/front3
/front
Main relay

Electric fan
Fan High Speed Relay
Fan Low Speed Relay
Mando MGH-25 Anti-Lock Brake
System
User’s Manual
 CONTENT
Common Abbreviations and Acronyms in This Manual………………………………… 2
I. Product Instruction………………………………………………………………………. 3
1． ABS Overview ……………………………………………………………………….. 3
1.1 System Function…………………………………………………………………… 3
1.2 Comparison between with and without ABS braking effects…………………... 3
2． System Structure…………………………………………………………………….. 5
3． System Functioning Theory…………………………………………………………. 6
3.1 ABS Control Theory………………………………………………………………… 6
3.2 ABS Control Mode……………………………………………………………….. 6
3.3 EBD Control Mode……………………………………………………………….. 9
II. Removal and Installation………………………………………………………………... 10
1． Spare Part Supply Status…………………...………………………………………. 10
2． Notices for Removal and Installation………………………………………………. 10
3． HECU Replacement…………………………………………………………………. 12
III. Trouble Diagnosis and Troubleshooting………………………………………………. 14
1． Checking Sequence…………………………………………………………...……… 14
2． Common Trouble Diagnosis and Troubleshooting of MGH-25 ABS……...……… 14
2.1 Checking of ABS and EBD Warning Lamp……………………...….…………... 14
2.2 Table for Common Troubles…………………….……………………………….. 14
2.3 Trouble Code Readout and Deletion without Trouble Diagnosis Instrument… 15
2.4 Trouble Checklist of Trouble Code……………………………………………… 17
2.5 Trouble Checklist without Trouble Code…………………...…………………… 25
IV. Air Discharge and Oil Refill……………………………...…………………………….. 30
1. Regular Operation Procedure………………………… ……………………………. 30
2. Checking Device……………………………………...………………………………… 30
3. Notices for Air Discharge and Oil Refill………………………………………………… 30
4. Determination Method for Vehicles with Air Discharge Trouble……...……………….. 31
5. Measures in Event of Troubles during Air Discharge and Oil Refill
(for internal dry status of brake system)………………………………………………… 31
6. Measures in Event of Trouble during Checking and ABS Functioning Test
(for internal wet status of brake system) ……………………………………………… 32
Annex I Malfunction Cases and Incorrect Repair Cases…………………………….. 34
Annex II ABS Basics……………………………………………………………..……... 36
Annex III ABS Internal hydraulic Flow Diagram………………………………….… 37
Annex IV Connector Pin Layout of MGH-25 ABS ECU……………….………….… 37

Page 1 of 38
 Common Abbreviations and Acronyms in This Manual

FL——Front Left

FR——Front Right

RL——Rear Left

RR——Rear Right

ABS——Anti-lock Brake System

EBD——Electronic Brake Distribution

ECU——Electronic Control Unit

HU、HCU——Hydraulic (Control) Unit

HECU——ECU+HCU

LPA——Low Pressure Accumulator

MCP——Master Cylinder Primary, one of two outlet of master cylinder. P refers to

primary.

MCS——Master Cylinder Secondary, one of two outlet of master cylinder. S refers to

secondary

SDL——Serial Data Link

Page 2 of 38
I. Product Instruction
1． ABS Overview
1.1 System Function
① Promotion of vehicle stability;
② Guarantee of vehicle steering ability;
③ Guarantee of shortest brake distance.

1.2 Comparison between with and without ABS braking effects

Without ABS With ABS

Braking on Bisectional Roads (Split)

Without ABS With ABS

Evading the obstacles during braking

Page 3 of 38
1.3 Tire Dynamic Characteristics

Slip Ratio

Brake Force

Steering Force

Slip Rate [%]

Page 4 of 38
 2． System Structure

Motor

Including:

The sensor will calculate the speed and acceleration/deceleration

of four wheels and judge the skid status of the wheels and
Electronic Control Unit therefore drive the electromagnetic valve and motor, control the
pressure increment and pressure reduction, maintain the status,
and etc.
The basic hydraulic circuit is comprised of the 1st circuit and the
2nd circuit that is active only when the ABS is functioning and is
the integral part that controls the hydraulic parts transmitted to
various wheels.
Depending on the transmitted signal output of the sensor, the
Hydraulic Unit
ECU performs the calculation and judges the skid status to
determine if it’s necessary to run the ABS. Therefore, depending
on the control procedure of the ECU, the electromagnetic valve
and the motor will be started to control the pressure increment
and pressure reduction, maintain the status, and etc.
In order to make the ECU to calculate the speed and acceleration/
Sensor deceleration of the four wheels, it always transmits the revolution
measurement of the gear ring to the ECU.
When the ABS is functioning, the motor will rotate following the
Motor ECU signal and convert the rotation movement into linear
reciprocated movement via the bearing to circulate the brake oil.

Page 5 of 38
 3． System Functioning Theory
3.1 ABS Control Theory

ABS Control Range Slip Ratio

Start
Start Body Speed – Wheel Speed
Pressure Pressure
Increment Reduction
Body Speed

Tire braking force (μs)

Tire transversal friction force (μs)

Skid Ratio

λ= 100%: The status that the wheels

λ= 0%: The status that the brake is
are locked
not functioning

3.2 ABS Control Mode

① Functioning Status of General Brake
For the vehicles equipped with ABS, if the braking pressure applied onto the wheels is not enough
to lock the wheels, the pressure generated by the general pump will transmit to the wheel branch
pump via the normal open valve to obtain the braking effects. When it’s unnecessary for further
braking, the driver will reduce the pressure on the brake pedal and then the brake liquid of various
wheels will return to the general pump to reduce the braking pressure.
Solenoid Valve Power Status Solenoid Valve Status
Normal Open Valve (NO Valve) OFF Open
Normal Close Valve (NC Valve) OFF Close

Page 6 of 38
② ABS Functioning (Pressure Reduction) Status
For the vehicles equipped with ABS, if the applied braking pressure is too big, the wheels will
have rapider deceleration than that of vehicle body, which will be ready to result the lock of the
wheels. Under such case, the ECU will transmit the code for wheel pressure reduction to the HCU,
namely turn off the normal open valve and turn on the normal close valve to reduce the pressure of
wheel branch pump. In such case, the brake oil released by the wheel branch pump is temporarily
stored in the low pressure accumulator (LPA). The brake oil stored in the LPA will be sucked
back to the general pump by the oil pump started following the rotation of the motor. The brake
liquid will return to the high pressure accumulator (HPA) in the pipeline and reduce the high
pressure pulse generated by the running of the oil pump by means of the orifice hydraulic
resistance.

Solenoid Valve Power Status Solenoid Valve Status

Normal Open Valve (NO Valve) ON Close
Normal Close Valve (NC Valve) ON Open

③ ABS Functioning (Maintaining) Status

When the branch pumps of the wheels are applied with proper pressure via the pressure reduction
or pressure increment, the normal open valve and the normal close valve will be turned off to
maintain the pressure of the wheel branch pumps. For the operations mentioned in above ② ~ ④,
depending on that wheels are locked or not, the ABS will function till the vehicle is fully stopped
and therefore the safety and steering capability of the vehicle are guaranteed.

Solenoid Valve Power Status Solenoid Valve Status

Normal Open Valve (NO Valve) ON Close
Normal Close Valve (NC Valve) OFF Close

Page 7 of 38
④ ABS Functioning (Pressure Increment) Status
During the implementation of the pressure reduction, if the excessive brake liquid is drained or the
friction coefficient between the wheels and the road is increased, it’s necessary to increase the
pressure of various wheels. Under such case, the ECU will transmit the code for wheel pressure
increment to the HCU, namely turn on the normal open valve and turn off the normal close valve to
increase the pressure of wheel branch pump. During the implementation of the pressure reduction,
the brake liquid stored in the low pressure accumulator (LPA) will continue to rotate the motor to
drain the brake liquid under the pressure increment status. In such case, the brake liquid is supplied
to branch pump of various wheels via the general pump and normal open valve. The brake liquid
will return to the high pressure accumulator (HPA) in the pipeline and reduce the high pressure pulse
generated by the running of the oil pump by means of the orifice hydraulic resistance.

Solenoid Valve Power Status Solenoid Valve Status

Normal Open Valve (NO Valve) OFF Open
Normal Close Valve (NC Valve) OFF Close

Page 8 of 38
 3.3 EBD Control Mode

In order to guarantee the operation stability, the EBD function is designed in such manner that front
wheels are stopped ahead of the rear wheels. As the front brakes undertake more works than that of
the rear brakes, it will cause that the rear wheels will be stopped firstly when apply with same braking
pressure. In order to preventing the occurrence of above thing, a device to reduce the braking pressure
applied on the rear wheels under certain pressure is required, of which this function is fulfilled by the
pressure reducing valve (P-Valve). The special pressure reducing valve is not required for the vehicles
equipped with ABS as the procedure supplemented to the ABS will fulfill the control function on the
braking pressure of the rear wheels so as to effect the improvement of vehicle operation stability.

Page 9 of 38
II. Removal and Installation
1. Spare Part Supply Status
① Differentiation between Dry Type HECU and Wet Type HECU
The biggest differentiation between the dry type HECU and wet type HECU is that the no air
discharge is conducted in the 2nd circuit (namely the circuit from the normal close valve to the
general pump) of the dry type HECU. Therefore, when the spare part is of wet type HECU, it’s
only necessary to conduct the air discharge and oil refill in accordance with the regular brake
system after the replacement. When the spare part is of dry type HECU, besides that the air
discharge and oil refill are required in accordance with the regular brake system after the
replacement, it’s necessary to conduct the air discharge and oil refill to the 2nd circuit of the HECU.
In addition, for the appearance, the wet type HECU has the bolts for sealing purpose and the dry
type HECU has the protection film. The product label located on the motor is marked with the part
number of the products, through which the dry type HECU and wet type HECU can be
differentiated.
Take the S21 model for instance, the dry type Mando product number is BH601-086-00 and the wet
type Mando product number is BH602-386-00.

Dry Type Wet Type

② Notices
If the bolts on the wet type HECU are fallen off (such as during the transportation), besides that the
air discharge and oil refill must be conducted for 1st circuit, maybe it’s necessary to conduct the air
discharge and oil refill to the 2nd circuit.

2． Notices for Removal and Installation

① Notices for HECU Assembling

During the assembling of brake pipeline:

† Remove the protection film attached onto the HECU
before the operation.
† Confirm the pipeline of general pump and wheel branch
pump before the operation.
(General pump: MCP, MCS Wheel branch pump: FR,
FL, RR, RL)
† Confirm if the brake hose is tightened to 120~160
kgf·cm with special tool or torque wrench.
† Notice to keep away the impurity ingress into the
HECU hole and brake hose during operation.

Page 10 of 38
② Notices for HECU Bracket Assembling

During the assembling of HECU bracket:

† During the tightening of the bolt (3
pcs), it may cause the incorrect
Bracket
assembling due to the friction
resistance of the cushion pad. It’s Installation bolt
preferable to use the lubricating oil
with the physical properties that will
not impair the cushion pad. Bumper block

† Insert the bolts (3 pcs) onto the

cushion pad installed onto the bracket
before install to the HECU, which
will help the operation.
† Confirm if the bolts (3 pcs) are tightened to 80~100 kgf·cm with special tool or torque
wrench.

③ Notices for Installation of HECU and Bracket Assembly

During the installation to vehicle body:

† Attach the components of brake hose and
bracket to the HECU and install to the
vehicle body with the body fixing bolts.
† Confirm if the body fixing bolts are
tightened to 190~260 kgf·cm with special
tool or torque wrench.
† Again confirm if the pipeline installation
of general pump and wheel branch pump
is correct.
(General pump: MCP, MCS; Wheel branch pump: FR,
FL, RR, RL)
† Tighten the brake hose not fully tightened to the specified torque (120 ~ 160
kgf·cm) with special tool or torque wrench.
④ Other Notices

† Find out the trouble cause with diagnosis instrument before repair.
† The package of the spare parts should be unwrapped only before the installation.
† Only use the parts supplied by the original manufacturer.
† Notice the cleanliness during removal and only use the non-fuzz cloth for cleaning.
† Use the detergent not containing the mineral oil to clean the appearance before removal.
† Do not use the compressed air or move the vehicle when the system is opened.
† After the removal of the ABS assembly, plug various hydraulic outlets with plugs as soon as
possible.
† Remove other components interfering the operation.
† Use DOT#3 brake liquid.
† Immerse the seals with brake liquid, instead of engine oil or braking ointment.
† Check all hydraulic connectors for leakage.

Page 11 of 38
3． HECU Replacement
① When the vehicle is stopped, remove the 25-pin connector and harness wiring of the HECU
located within the engine compartment.

25-Pin Connector Used in MGH-25 ABS

(P/No：AMP 368482-1)

② Screw off in counter clockwise direction the 6 bolts (M10x1.0) connected to the HECU brake
hose with 11mm tool (wrench) (rotate in clockwise direction during refit). The tightening torque for
the brake hose is 120 ~ 160 kgf·cm.

③ Screw off in counter clockwise direction the 3 bolts or nuts connected to the bracket with
12mm tool (wrench) (rotate in clockwise direction during refit). The tightening torque for the fixing
bolts or nuts of the bracket is 190 ~ 260 kgf·cm.

④ After the removal of the product, screw off in counter clockwise direction the 3 embedded
bolts (M6x1.0) attached to the HECU with 5mm tool (hex wrench) (see the figure in next page).

Page 12 of 38
⑤ Screw off in counter clockwise direction the 6 bolts from the after-service HECU with 6mm
tool (hex wrench).

⑥ Screw on in clockwise direction 3 embedded bolts to assemble the after-service HECU and
the bracket with 5mm tool (hex wrench). The tightening torque for the embedded bolts is 80 ~ 100
kgf·cm.

⑦ With reference to above item ①~ ③, install the replacement after-service HECU to the
vehicle in reverse order.

Page 13 of 38
III. Trouble Diagnosis and Troubleshooting
1． Checking Sequence

Regular checking Checking of wheel Checking of valve Record checking

speed sensor and terminal result

• ECU ID determination • Sensor air gap determination • Valve status determination • Trouble code
• ECU trouble code • Sensor assembling status • Pipeline assembling status determination
determination determination determination • Trouble code record
• Warning lamp status
determination

2． Trouble Diagnosis and Troubleshooting of MGH-25 ABS

2.1 Checking of ABS and EBD Warning Lamp
Check if the ABS and EBD warning lamps are illuminated in accordance with following:
① Rotate the vehicle key to turn on the power. The ABS warning lamp will illuminate and then
go off in 3s.
② It indicates the trouble if the status mentioned in ① is not present and it’s necessary to
check the trouble code with reference to the trouble code checklist.
③ If the warning lamps are completely not illuminated, please refer to the trouble checklist
without trouble code.

2.2 Table for Common Troubles

Warning lamp
Position Cause Structure
ABS EBD
Incorrect assembling of Locked wheels and brake off-
brake hose tracking
Vehicle Brake oil leakage Poor start of ABS and EBD
Off Off
harness Incorrect wiring
Brake failure
installation
Air discharge trouble Deteriorated ABS performance
Motor Motor trouble ABS start failure On Off
Trouble of ECU power line Start failure of ABS and EBD
Trouble of valve power
Start failure of ABS and EBD
line On On
ECU Poor grounding of ECU Start failure of ABS and EBD
ECU trouble Start failure of ABS and EBD
Trouble of motor wire line ABS start failure On Off
In event of whichever trouble: ABS
On Off
Sensor open-circuit/short- start failure
circuit In event of both troubles: Start failure
On On
Speed of ABS/EBD
sensor Gear ring trouble, sensor In event of whichever trouble:
interference trouble, air gap On Off
Incorrect start of ABS
trouble
In event of both troubles: Start failure
On On
of ABS/EBD

Page 14 of 38
2.3 Trouble Code Readout and Deletion without Trouble Diagnosis Instrument
① Purpose and condition of trouble code readout without trouble diagnosis instrument
If without the trouble diagnosis instrument, it may display the trouble status of the ABS via the
ABS warning lamp and read out the trouble code to facilitate the trouble determination and
troubleshooting. In such case, the trouble code will be displayed in 2-digit number. Please refer to
the numbers in parentheses in the trouble checklist of trouble code in succeeding section 2.4.
The service conditions are as follows:
† Vehicle speed below 2km/h;
† Without connection of trouble diagnosis instrument;
† The line L (namely the pin 7 of interior diagnosis socket) should be always grounded
during the diagnosis process.

In addition, at finish of the trouble code readout, restore the ECU status of the ABS to the normal
mode (previously, it’s the diagnosis status), of which the method is as follows: At finish of the
diagnosis operation, disconnect the grounding status of the line L, rotate the key to power off status,
and then re-connect.
② Readout method of trouble code without trouble diagnosis instrument
Read out the trouble code in accordance with following procedure when the service conditions for
trouble code readout without trouble diagnosis instrument are met:

Line L

Ignition
Switch

ABS
warning
lamp

The display will be repeated without any new trouble code.

The steps in above figure are respectively:

A. Rotate the vehicle key to power on position after the line L is grounded;
B. When the ABS warning lamp illuminates and lasts for 3s, it indicates the start of
diagnosis;
C. When the ABS warning lamp is off for 3s, it indicates that it enters into the
trouble code display phase;
D. Trouble code display and readout;
E. Wh en th e AB S w ar ni n g l a mp i s o ff fo r 3 s , i t i n di c ate s t ha t i t ent er s i nt o
next troub le display phase or cir culated disp lay phase;
F. The display and readout of new trouble code and the circulated display of last trouble code.

Page 15 of 38
 The meaning of symbols in the figure is as follows:

Code Symbol Description Duration

T1 The symbol for diagnosis start. The warning lamp starts flashing 3.0s
For differentiation of the duration of various trouble codes during
T2 3.0s
the display of multi trouble codes
T3 Flashing interval of warning lamp at the presence of trouble code 0.5s
For differentiation of the interval of various digits of trouble code
T4 during the display of certain trouble code (for this interval, the 1.5s
first digit is for tens digit and the second digit is for ones digit)

Take the process shown in above figure for instance. Within the display span of the first trouble code,
before the presence of T4 (namely, 1.5s before the off of the warning lamp), since the warning lamp
flashes twice (the duration for each on and off is both T3, namely 0.5s), the first digit of the 2-digit
trouble code (tens digit) is at 2; after the presence of T4 (namely 1.5s after the off of the warning
lamp), since the warning lamp flashes once, the second digit of the 2-digit trouble code (ones digit) is
at 1. After that, the warning lamp will be off for 3s (namely T2 duration). Therefore, the display of
first trouble code is completed with the trouble code of 21. The detailed description of the trouble is
shown in the trouble code checklist in section 2.4. Also, the second trouble code of 22 can be
obtained.

③ Deletion of trouble code without trouble diagnosis instrument

After the trouble code readout and troubleshooting based on the trouble code checklist, it’s necessary
to delete the previous trouble code before the re-checking of the trouble code. The condition for
trouble code deletion is same with that of the trouble code readout. The detailed operation method is
as follows:

Line L

Ignition switch
Pedal depressing
Brake pedal
Pedal releasing
ABS warning lamp 3s 3s

Deletion period

Within Within Within 2sWithin 2sWithin 2s Within 2s

1s 2s (2 times)(3 times)(4 times) (5 times)
(1 time)

The steps in the above figure are respectively as follows:

A. After the brake pedal is depressed, ground the line L and rotate the vehicle key to the power on
position;
B. The ABS warning lamp illumination and go off in 3s;
C. Start to release the pedal within 1s after the ABS warning lamp goes off;
D. After the pedal is released for approximate 1s, re-depress the pedal for approximate
1s. Repeat the above operation for 5 times. During this operation, the warning lamp will
not be illuminated;
E. The ABS warning lamp illuminates and lasts for 3s. During this period, the trouble
code within this process will be deleted.

At the finish of the trouble code deletion, restore the ECU status of the ABS to the normal mode,
Page 16 of 38
 of which the operation method is same with that of the trouble code diagnosis.
In addition, when the ECU of the ABS has no trouble code, ground the line L and rotate the
key to the power on position. The flashing of the ABS warning lamp is conducted in
accordance with the type in following figure, of which the symbol meaning is same with the
foregoing section.

Line L

Ignition
Switch
ABS warning
lamp

2.4 Trouble Checklist of Trouble Code

① Contents of Trouble Code

Trouble Trouble
Contents Contents
code code
C1 200 Open-circuit/short-circuit of left C1 206 Open-circuit/short-circuit of left rear
(11) front sensor (31) sensor
C1 201 Interference of left front sensor or C1 207 Interference of left rear sensor or gear
(12) gear ring (32) ring
C1 202 C1 208
Air gap error of left front sensor Air gap error of left rear sensor
(13) (33)
C1 203 Open-circuit/short-circuit of right C1 209 Open-circuit/short-circuit of right rear
(21) front sensor (41) sensor
C1 204 Interference of right front sensor C1 210 Interference of right rear sensor or
(22) or gear ring (42) gear ring
C1 205 C1 211
Air gap error of right front sensor Air gap error of right rear sensor
(23) (43)
C1 101 Battery voltage too high (above C2 112 Trouble of electromagnetic valve fuse
(51) 17V) (54) or electromagnetic relay
C1 102 Battery voltage too low (below C2 402
Trouble of motor fuse or motor
(52) 9.4V) (55)
C1 604 Trouble of ECU internal circuit or
(53) electromagnetic valve coil

Page 17 of 38
 ② Trouble checklist of trouble code
Table 1
C1 200(11) C1 203(21) Note: If the malfunctions corresponding to
Trouble Code
C1 206(31) C1 209(41) more than 2 trouble codes can be determined,
Open-circuit/short-circuit of sensor: after the trouble codes are deleted (erasable
At short-circuit or open-circuit trouble codes), drive the vehicle to above
of batter y anode or cathode of 40km/h to determine the malfunctions to that
Possible Case
sensor. the trouble codes correspond and check in
accordance with the registered trouble codes
(determine the same one trouble code).

Harness Sensor

Sensor Head
Remove the connector from the
harness and sensor, confirm the
assembling status, and check the
pins for deviation

Correct the connector

No pins and correctly
Is status good?
assemble the connector

Yes

Determine if the two lines between

harness side pin A and connector B
Troubleshooting of sensor assembly are powered
Flow

No Determine and repair

Is powered on? wiring broken portion or
replace wiring

Yes
Replace sensor

Is the problem
still present?

Yes

Replace HECU

Page 18 of 38
 Table 2
Trouble Code C1 202(13) C1 205(23) Note: ①The air gap refers to the gap between
C1 208(33) C1 211(43) the gear ring and the sensor;
Possible Case Air gap error: ② If the malfunctions corresponding to more
Air gap too big or self short-circuit than 2 trouble codes can be determined, after
of sensor (resistance value at 0) that the trouble codes are deleted (erasable trouble
results no signal or the gear ring codes), drive the vehicle to above 40km/h to
not properly installed. determine the malfunctions to that the trouble
codes correspond and check in accordance
with the registered trouble codes (determine
the same one trouble code).
Troubleshooting
Flow

Replace sensor

Is problem No
still present? Checking
complete

Yes

Replace HECU

Page 19 of 38
 Table 3
Trouble Code C1 201(12) C1 204(22) Note: ① The sensor signal is not uniform
C1 207(32) C1 210(42) when the gears are adhered with engine oil
and the impurities such as slag;
Possible Cause Interference of gear ring or sensor: ② The air gap refers to the air gap between
Occurred when installed with non- the gear ring and the sensor;
standard specification gear rings. ③ If the malfunctions corresponding to more
than 2 trouble codes can be determined, after
the trouble codes are deleted (erasable trouble
codes), drive the vehicle to above 40km/h to
determine the malfunctions to that the trouble
codes correspond and check in accordance
with the registered trouble codes (determine
the same one trouble code).
Troubleshooting
Flow

Replace sensor

Is problem No
still present? Checking complete

Yes

Replace HECU

Page 20 of 38
 Table 4
Trouble C1 101(51) C1 102(52) Note: If the malfunctions corresponding to more
Code than 2 trouble codes can be determined, after the
Possible Abnormal battery voltage: trouble codes are deleted (erasable trouble codes),
Cause Occurred when the voltage is too high or too drive the vehicle to above 40km/h to determine the
low malfunctions to that the trouble codes correspond
and check in accordance with the registered
trouble codes (determine the same one trouble
code).

Remove harness side

connector and measure the
voltage between pin 4 (+) and
8(-) and between pin 4(+) and
24(-) when the entire vehicle
circuits are on.

No
Is between ① Measure the voltage
9.4V~17V? between battery terminal
(+) and (-)
Yes

Confirm the assembling No Measure the resistance

status and pin displacement between the harness side
of harness side connector pin
Is below 9.4V? connector pin 4(+) and
4, 8, and 24 battery (+) terminal
Yes
Troubleshooting Flow

Check and replace No

battery Check and
Is below 1Ω? replace wiring
Yes
No
Adjust connector pins
Is status good? Correctly assemble Confirm and check
connectors grounding status of harness
side connector pin 8 (-),
Yes and 24 (+)

Replace HECU No
Adjust status of
Is status good? grounding terminal

Yes
Measure the voltage between
pin 4 (+) and 8(-) and
between pin 4(+) and 24(-)
when the entire vehicle
circuits are on.

No
Re-check from
Is above 17V? item ①
Yes

Replace AC
generator

Page 21 of 38
 Table 5
Trouble Code C2 402(55) Note: If the malfunctions corresponding to more
Possible Cause Malfunction of motor fuse/motor than 2 trouble codes can be determined, after the
trouble codes are deleted (erasable trouble codes),
drive the vehicle to above 40km/h to determine
the malfunctions to that the trouble codes
correspond and check in accordance with the
registered trouble codes (determine the same one
trouble code).
Troubleshooting
Flow
(1) After the harness side
connector is removed, confirm
if the harness side pin 25 and
the grounding wire are
connected

No Confirm if the harness side

Is it on? pin 25 and the terminal in the
Yes fuse box are connected

Check and replace No

the wiring of harness Check and replace the wiring of
Is it on?
harness side pin 25
side pin 25.
Yes

Confirm if the valve fuse

(30A) in the fuse box is
broken

No
Is fuse (30A) Check and replace the valve fuse
normal?

Yes

Confirm the assembling status and

pin displacement of pin 25 of
harness side connector

No
Adjust the connector pins and
Is status good? correctly assemble connector
Yes

Forced drive the HECU with

Is status good?
diagnosis instrument (valve relay and
motor start)

No
Is forced drive good? Replace HECU

Yes

Re-check from item ①

Page 22 of 38
 Table 6
Trouble Code C2 112(54) Note: If the malfunctions corresponding to more
Possible Cause Malfunction of valve fuse and relay: than 2 trouble codes can be determined, after the
a) Broken of primary relay or fuse trouble codes are deleted (erasable trouble codes),
b) Short-circuit of primary relay drive the vehicle to above 40km/h to determine
the malfunctions to that the trouble codes
correspond and check in accordance with the
registered trouble codes (determine the same one
trouble code).
Troubleshooting
Flow
(1) After the harness side
connector is removed, confirm
if the harness side pin 25 and
the grounding wire are
connected

No
Confirm if the harness side
Is it on?
pin 25 and the terminal in the
Yes fuse box are connected

Check and replace

No Check and replace the wiring of
the wiring of harness Is it on?
harness side pin 25
side pin 25.
Yes

Confirm if the valve fuse

(30A) in the fuse box is
broken

No
Is fuse (30A) Check and replace the valve
normal? fuse
Yes

Confirm the assembling status and

pin displacement of pin 25 of
harness side connector

No
Adjust the connector pins and
Is status good? correctly assemble connector

Yes

Forced drive the HECU with

diagnosis instrument (valve
relay and motor start)

No
Is forced drive good? Replace HECU

Yes

Re-check from item ①

Page 23 of 38
 Table 7
Trouble Code C1 604(53) Note: If the malfunctions corresponding to
Possible Cause Malfunction of ECU internal circuit more than 2 trouble codes can be determined,
and valve coil after the trouble codes are deleted (erasable
trouble codes), drive the vehicle to above
40km/h to determine the malfunctions to that
the trouble codes correspond and check in
accordance with the registered trouble codes
(determine the same one trouble code).
Troubleshooting
Flow

Remove the harness side connector and measure

the resistance between the harness side connector
pin 8 (-) and grounding wire and between the pin
24 (-) and grounding wire

No
Confirm and check the grounding
Is it below 1Ω? status between the harness side
connector pin 8(-) and 24(1)
grounding terminal.
Yes

Replace HECU

Page 24 of 38
 2.5 Trouble Checklist without Trouble Code
Table 1
Trouble
The ABS warning lamp doesn’t illuminate when the engine is started
Evidence
Possible Cause ● Burn of fuse ● Burn of ABS warning lamp bulb
● Open-circuit of power line ● Damage of ABS warning lamp control
Troubleshooting
Flow
Check ABS warning
lamp fuse in fuse box

No
Is fuse normal? Replace fuse

Yes
Check fuse
socket of fuse
box

No
Is socket normal? Repair fuse socket

Yes

Remove the harness side

connector and check the ABS
warning lamp when the entire
vehicle circuits are on.

No
Does ABS Check if the ABS Yes
Is bulb Replace bulb
warning lamp warning lamp bulb is damaged?
illuminate? damaged?

Yes No
After the harness side connector
is removed, check for short- Check if warning lamp
circuit between the harness side power circuit of ABS
pin 16 and warning lamp drive harness and grounding
component wire are disconnected

No
Short-circuit? Is it normal? Replace
harness
Yes Yes

Check and replace the Check warning lamp power

wiring of harness side circuit and grounding
circuit connector
pin 16

No
Is it normal? Repair
connector
Yes
Check and replace
warning lamp drive
component

Page 25 of 38
 Table 2
Trouble
The ABS warning lamp constantly illuminates after the vehicle start
Evidence
Possible Cause ● Damage of ABS warning lamp control
● Open-circuit of ABS warning lamp control circuit
● ECU damage of ABS

Troubleshooting
Flow
After the harness side connector is
removed, confirm if it's powered
between the harness side pin 16 and
warning lamp drive component.

No
Check and replace
Is it powered? wiring of harness side
pin 16
Yes

Connect the harness side pin 16 to

the grounding wire when the entire
vehicle circuits are on.

No
Check and replace
Is warning lamp off? warning lamp drive
component
Yes

Replace HECU

Page 26 of 38
 Table 3
Trouble
Abnormal functioning of ABS
Evidence
Possible Cause ● Damage of sensor ● Damage of gear ring
● Improper installation of sensor ● Damage of wheel bearing
● Problem of sensor harness ● HCU damage of ABS
● Impurity adherence on sensor ● ECU damage of ABS
Troubleshooting
Flow
Is the sensor correctly
installed?
No

Re-install the sensor

with correct method

No
Is problem Checking complete
still present?

Yes

Replace sensor

No
Is problem
Checking complete
still present?

Yes
No
Check if the ABS ECU Replace HECU or
socket and connector
are normal connector

Yes

Replace harness, connector or

HECU

Page 27 of 38
 Table 4
Trouble
Brake pedal travel too long
Evidence
Possible Cause ● Improper adjustment of handbrake
● Leakage of brake liquid
● Severe wearing of brake friction disc
● Leakage of normal close valve
● Air in the system
Troubleshooting
Flow

Check hydraulic pipe

connector for leakage

No
Tighten pipe connector to
Having leakage?
120~160kgf.cm
Yes

Check wearing of brake disc

No
Is it normal? Replace brake disc
Yes

Check handbrake regulator

No
Is it normal? Replace handbrake regulator

Yes

Air discharge checking

No
Is it normal? Re-conduct the air
discharge
Yes

Replace HECU

Page 28 of 38
 Table 5
Trouble Without diagnosis code output (communication failure with trouble diagnosis
Evidence instrument)
Possible Cause ● Problem of diagnosis instrument
● Burn of fuse
● Broken of diagnosis line or loosening of connector
● ECU damage of ABS
Troubleshooting
Flow
Confirm the connection
between the diagnosis
instrument connector and
vehicle diagnosis connector

No
Is it normal? Correctly install the
connector
Yes
After the harness side connector is
removed, confirm if it’s powered
between the harness side pin 7 and
vehicle diagnosis connector pin 7

No Check and replace

Is it powered? wiring of harness side
pin 7
Yes

Confirm if the ABS ECU

fuse (10A) in the fuse box
is burnt?

No
Is fuse (10A) Check and replace ABS
normal? ECU fuse

Yes

Correctly connect the harness

side connector and confirm
the communications.

No
With Check and replace
communications? diagnosis instrument
Yes
After the trouble number is
determined, take measures based
on the troubleshooting for
various trouble numbers.

Page 29 of 38
IV. Air Discharge and Oil Refill
1. Regular Operation Procedure

Add brake fluid

On
Off

Vacuum
On
Off

Motor
On
Off
Normal
Close Valve On
Off

Procedures

The regular operation procedure of air discharge and oil refill is shown in the figure, of which:
A : Move the vacuum device and brake oil refill device;
B : Start after connected with vacuum and brake oil refill device and SDL;
st
C : Drive normal close electromagnetic valve and apply the 1 vacuum;
D : Excessive leakage test;
st
E : Minor leakage test after the 1 vacuum cut-off;
nd
F : Applicable for 2 vacuum and drive motor;
G : After the oil refill and maintaining of pressurization on the brake oil, relieve the brake oil pressure, stop
the normal close electromagnetic valve and motor, and adjust the brake oil level;
H : Disconnect the vacuum device and brake liquid refiller;
I : Screw on the oil reservoir lid/disconnect the SDL;
J : Transfer to next step.

2. Checking Device
① The vacuum supplied to the oil reservoir should be as lower as possible, provided that the oil gun must
supply at least below 1mm Hg vacuum.

② Confirm if the air discharge screw portion of the rear wheel hydraulic device (drum brake or brake
caliper) forms the vacuum within the specified period. (It should be below 5~10mm Hg after connected
with vacuum for 20~25s).

③ Confirm if the working voltage supplied to the HECU is at specified 10~12V.

④ Confirm the circulation time (C/T). Confirm the working time setting of the electromagnetic valve
meets with the specified value.
† C/T< 90: Run the electromagnetic valve continually;
† 90≤C/T≥180: Start the electromagnetic valve for 2s and stop the electromagnetic valve for 2s.
continually repeat above cycles;
† C/T>180: The total running period setting of the electromagnetic valve is below 90s.

3. Notices for Air Discharge and Oil Refill

Page 30 of 38
 ① During the refilling of brake oil, if the refilling pressure is not maintained for certain period or
above, the oil level within the oil reservoir will lower at the finish of the refilling. Therefore, it’s
required to refill more brake oil or maintain the refilling pressure for certain period.

② The time period marked in the regular operations refers to the general circulation period.

③ The inside of after-service HECU is at moisture status, therefore, it may not conduct the air
discharge mode operation (see succeeding item 5⑥ for the definition of air discharge mode) but
directly conduct the air discharge operation on all wheels (However, in order to meet with the
performance and pedal comfort, it’s preferable to conduct the air discharge mode operation).

④ During the air discharge mode operation, the voltage supplied to HECU is preferably at
10~12V. However, during the use of checking devices, it will be OK to use the vehicle amounted
battery. (The repeated air discharge mode operation with high voltage may damage the coil of ECU
components).
4. Determination Method for Vehicles with Air Discharge Trouble
Differentiation Leakage test
ECU functioning or
Excessive Minor Note
not
Category leakage leakage
Normal functioning, no separate
Case 1 Normal functioning O.K O.K
repetition required
Abnormal functioning, separate
Case 2 Normal functioning O.K N.G
repetition required
Abnormal functioning, separate
Case 3 Normal functioning N.G N.G
repetition required
Abnormal functioning, separate
Case 4 Not functioning O.K O.K
repetition required
Abnormal functioning, separate
Case 5 Not functioning O.K N.G
repetition required
Abnormal functioning, separate
Case 6 Not functioning N.G N.G
repetition required

† Case 1 : The status at finish of normal functioning.

† Case 2 : The status that the connection of brake (HECU hole portion/brake pipe/brake
hose) is poor and therefore needs rework.
† Case 3 : The status same with Case 2, but it may cause the status incapable of
repetition when the leakage is really severe.
† Case 4 : Internal circuit air discharge trouble of HECU. It's the status necessary for
repetition as the ABS may cause the sponge phenomenon after functioning for one time.
† Case 5 : The comprehensive trouble of Case 2 and Case 4. The status necessary for
repetition.
† Case 6: The status similar to Case 5, but it may cause the status incapable of repetition
when the leakage is really severe.

5. Measures in Event of Troubles during Air Discharge and Oil Refill (for internal dry
status of brake system)
① Implementation of trouble determination. It’s required to determine the connection portions of
all components from the general pump to the wheel branch pump: HECU hole portion, connection
portion of brake pipe, connection portion of brake hose, brake caliper and the air discharge screw
portion of brake, and etc.
② After the determination of the trouble, re-assemble in accordance with the provisions in order
to avoid the further occurrence of leakage.
③ Connect the repetition device to the 25-pin connector of the ECU or connect the checking
device to the line K (pin 7). Use the specific wiring to connect to the connectors. During the
connection to line K (pin 7), make the vehicle at power on or start status. The oil reservoir of the
general pump is connected with the device for continual supply of brake oil or it’s required that the
oil reservoir should have enough oil during the supply of brake oil.
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④. Check the HECU with repetition device or checking device and determine the existence of
trouble code. If with trouble code, firstly conduct the operation for deletion of the trouble code (if
the trouble in above item ① is not determined, it’s necessary to determine the existence of
trouble code). When the trouble code can’t be deleted, operate with reference to the Trouble
Checklist of Trouble Code in section 2.4 (In case of trouble of HU, motor and ECU, the air
discharge and oil refill can’t be conducted at the inside of the HECU).

⑤ After the brake pedal is depressed, open the air discharge screw attached onto the wheel brake
caliper or drum brake to discharge the air. Conduct this operation on all wheels, till that the brake
oil discharged from the air discharge screw is free of air and the brake pedal is properly rigid. Refer
to the operation in item ⑩ in using the repetition device capable of vacuum formation and
refilling of brake liquid.

⑥ Conduct the air discharge mode by means of the repetition device or the checking device. If
there has no reaction force when the brake pedal is depressed, then repeat the operation of pedal
depressing and pedal releasing, till the air discharge mode is completed (air discharge mode: repeat
the start in 2s interval, stop the normal close valve of HECU for 1min, and continually drive the
motor. The repeated operation of pedal depressing and pedal releasing is conducted within the
period of normal close electromagnetic valve and motor drive).

⑦ The operation in item ⑤ (air discharge) should be repeated for all wheels.

⑧ Measure the brake pedal travel. If not meet with the provisions, repeat the operations in item
⑥ (air discharge mode) and item ⑤ (air discharge). If the brake pedal travel doesn't meet with
the provisions after the air discharge mode and air discharge are repeated for above 10 times,
replace with after-service HECU (wet type) and then repeat the operations from the beginning.

⑨ Connect the repetition device and checking device to the HECU and again determine the
existence of trouble code. If with trouble code, delete the trouble code and then disconnect the
repetition device or checking device.

⑩ During the use of other repetition devices (the equipment capable of vacuum formation and
liquid refilling), the implementation method is as follows:
† Conduct in accordance with the contents in above item ①～④;
† When the vacuum pump is sufficiently driving for approximate 60s, the inside of brake
system will form the vacuum status.
C Start the operation of air discharge mode in above item ⑥ 10s before the vacuum cut-off.
C Without the repeated operations of pedal depressing and pedal releasing.
† Conduct the brake liquid refilling operation (above 7bar/100Psi) for above 20s at the same
time of vacuum cut-off.
† Complete the brake liquid refill and air discharge mode.
† Conduct the operation based on the contents in above item ⑧～⑨.

6. Measures in Event of Trouble during Checking and ABS Functioning Test (for internal
wet status of brake system)
① Connect the repetition device or checking device. The following conditions must be
guaranteed:
† Use the specific wiring while connecting to the 25-pin connector of ECU.
† The vehicle should be at power on status or start status while connecting to line K (pin
7).
† The oil reservoir of the general pump is connected with the device for continual supply
of brake oil or it’s required that the oil reservoir should have enough oil during the
supply of brake liquid.

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② Check the HECU with repetition device or checking device and determine if it has trouble
code.
† If with trouble code, firstly conduct the operation to delete the trouble code.
† If the trouble code can’t be deleted, implement with reference to section 2.4 “trouble
checklist of trouble code” (If the HU, motor or ECU has trouble, the inside of HECU
can’t conduct the air discharge and oil refill).

③ After the brake pedal is depressed, open the air discharge screw attached on the wheel brake
caliper or drum brake to discharge the internal air. It's required to conduct this operation on all
wheels, till that the brake oil discharged from the air discharge screw is free of air and the brake
pedal is properly rigid.

④ Conduct the air discharge mode by means of the repetition device or the checking device. If
there has no reaction force when the brake pedal is depressed, then repeat the operation of pedal
depressing and pedal releasing, till the air discharge mode is completed

⑤ The operation in item ③ (air discharge) should be repeated for all wheels.

⑥ Measure the brake pedal travel. If not meet with the provisions, repeat the operations in item
④ (air discharge mode) and item ③ (air discharge). If the brake pedal travel doesn't meet with the
provisions after the air discharge mode and air discharge are repeated for above 10 times, replace
with after-service HECU (wet type) and then repeat the operations from the beginning.

⑦ Connect the repetition device and checking device to the HECU and again determine the
existence of trouble code. If with trouble code, delete the trouble code and then disconnect the
repetition device or checking device.

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Annex I Malfunction Cases and Incorrect Repair Cases
1. HECU Incorrect Repair Cases
① HECU replacement relating to ABS functioning noise
The HECU replacement case that deemed the noise of electromagnetic valve and motor as the
malfunction during the functioning of the ABS.
† During the functioning of ABS, the noise generated during the relieving or enhancing
of the braking pressure on various wheels is of normal functioning status. The noise
level will vary depending on the braking pressure applied on various wheels, other than
the product malfunction. Therefore, we should persuade the customers to understand
that.
† When the vehicle reaches 10km/h speed at the first time after vehicle start, the sensitive
customers may hear the noise at the time when the ECU diagnoses the motor drive,
which is also the normal functioning of the ABS.

② HECU replacement relating to EBD functioning noise

The HECU replacement case that deemed the clattering noise of rear wheels that other than
the ABS functioning noise during the braking as the malfunction.
† The ABS is also equipped with EBD function, which will effect the relieving of
braking pressure on the rear wheels when the rear wheels are locked ahead of the front
wheels. The noise generated during the above mentioned process is of normal
functioning status.

③ HECU replacement relating to braking off-tracking

HECU replacement case due to the vehicle braking off-tracking towards one side during the
braking.
† ABS is the braking assisted device that functioning in such manner that the ECU will
calculate the speed of various wheels in order to maintain the best braking force and
control stability during the braking. In the event of malfunction of the HECU, the ECU
will illuminate the warning lamp by means of the diagnosis. Therefore, in the event of
braking off-tracking without the illumination of ABS warning lamp, it’s necessary to
check other braking hydraulic devices.
† In the event of incorrect assembling of the braking hose, the braking off-tracking may
occur during the functioning of the ABS.

④ Replacement case that the ABS is functioning during barking at low speed (below 40km/h)
HECU and sensor replacement case that the ABS is always functioning during the braking at
low speed.
† During the braking at low speed, the ABS may also function depending on the road
conditions and braking pressure. If the ABS is always functioning at each time, it’s
necessary to check if the sensor air gap of various wheels is too large, if it has
interference with the gear ring, and if the tooth shape of the gear ring is damaged.
† Air gap adjustment method. For the improper air gap, after the determination of the
parts related to the problem, replace or grind the installation surface (junction portion)
of the sensor to the specified air gap; in the event of interference, place the thin gasket
onto the sensor installation surface so as to adjust to the specified air gap.

2. Incorrect Repair Cases for Wheel Speed Sensor

① Open-circuit and short-circuit related to sensor
The sensor replacement case without product checking when the ABS warning lamp is
illuminated and the trouble code of the vehicle is determined.
† The ABS trouble code is prepared based on the ABS products. Therefore, during the
open-circuit or short-circuit of the sensor, it’s necessary to conduct the problem
checking, such as confirm the connection status from the ECU to the wiring and
connectors of the sensor, measure the sensor resistance, and etc. During the
malfunction checking of sensor, it’s preferable to use the tetrastyle jack, which will
facilitate the confirmation of short-circuit problems such as the pinned wiring.

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 † The union status of the sensor must be checked before the removal of the connectors
of connecting wiring (such as incomplete union, pin displacement, with impurity, and
etc.)After confirm that the sensor resistance and head are free of abnormalities,
centrally check the wiring and connectors.

② Notices for sensor checking

Case of sensor head line break arisen from over-pulling of sensor cable.
† When the connectors are removed during the checking of sensor, the instantaneous
pulling of cable under the condition that the sensor head is fixed will cause the falloff
of the internal cable of the sensor head to cause line break problem. Therefore, during
the checking of sensor, do not pull the cable with the force above the specified one.
† Sensor head cable: It may be damaged when applied with above 12kgf tension force;
Cable at connectors: it may be damaged when applied with above 4.5kgf tension force.

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Annex II ABS Basics
Will the braking distance be shortened when equipped with ABS?
† The testing data show that the braking distance will be shortened on most road
conditions (approximately 5%~20%). However, under some special road conditions
(such as snowy road, non-asphalt road and rough road), the braking distance will be
lengthened. However, the steering stability can be guaranteed.

What’s the main objective of ABS?

† The main objective of ABS is to prevent the wheels to be locked, which has following
effects:
① Maintain the vehicle stability on roads during the braking
② Capable of controlling the vehicle driving direction during braking in order to avoid the
occurrence of the collision.
③ Maintain the best braking pressure, disregarding the driving skills of the driver.

Why is the ABS warming lamp illuminated?

† After the driver starts the vehicle, the warning lamp will be off when the automatic
diagnosis of ABS ECU shows no trouble. If the warning lamp is illuminated during
driving or the warning lamp is always on, it indicates the trouble of ABS. Please drive
your vehicle to the designated service station for checking of ABS as soon as possible.
However, when the warning lamp is illuminated that indicates the ABS trouble, the
brake system still has the basic braking capability.

Will there be free of accident when equipped with ABS?

† ABS is the one device capable of increasing the driving safety, rather than the device
used to avoid the accidents arising from the driving mistake or variation of traffic
conditions. Therefore, insist on the safe driving all along rather than the excessive
reliance on the ABS.

The vehicle will lean to one side during braking on the one-side-slippery road, is this
phenomenon caused by ABS?

† This phenomenon is resulted from the different friction coefficients between the left
and right wheels on the roads. Under such condition, the ABS will exert the special
effects on the stability of the vehicle body. However, even under such condition, make
sure to operate the steering wheel with car in order to avoid the occurrence of accidents.

The vehicle will present the slippery phenomenon before braking during the turning on the
slippery road, will the ABS function effectively when the brake pedal is depressed at that time?
† The ABS will function effectively to provide certain help depending on the vehicle
speed. However, under most conditions, the outward cornering force is really big due
to the vehicle inertia and therefore the body correction will have limit even the ABS is
functioning.
† Generally, the tires will be applied with two kinds of forces during cornering: One is
the force required by driving and braking; another is the force required for vehicle
steering and stability maintaining. In fact, the driving, braking and steering of the
vehicle are completed though the coordination of above two forces and the two forces
are in reverse ratio. Therefore, during the braking at cornering, the braking force will
be increased and the force required for steering and stability maintaining will be
reduced. The vehicles equipped with ABS will best coordinate these two forces. For the
vehicles without the ABS, the steering performance and the stability are really weak as
these two forces are not in good coordination.
† However, under the condition that the above two forces are really small (such as: off-
tracking due to excessive speed during the vehicle skid), the force for body correction
is really small. Therefore, the ABS will not exert the effects. In conclusion,
deceleration in advance and safe cornering is the best method.

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 Annex III ABS Internal hydraulic Flow Diagram

High pressure
accumulator

Normal
Open Valve

Normal
Close Valve Pump

Low-Pressure
Front Rear Accumulator Rear Front
right left right left

Annex IV Connector Pin Layout of MGH-25 ABS ECU

Power supply 2 Power supply 1

Grounding Grounding
wire wire
K line

Ignition

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 Harness side
connector
(Front view)

Grounding wire
Grounding wire

Rear right wheel sensor

Rear left wheel sensor

Front right wheel sensor

Front left wheel sensor

Wheel speed output

Drive circuit
instrument
diagnosis
Trouble

Note: “Ignition switch 1” refers to the status when the key is rotated
Warning lamp
Motor
cathode
to power on the vehicle but not to start the engine.
Motor pump

Ignition switch
anode

Brake lamp
Ignition switch 1

Motor anode

Valve anode
Brake switch

Motor
Motor module anode
Battery

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