Sensors
Sensors
Sensors
Sensors and
Troubleshooting
Sensor
1. General
Fig. 1 is outline of engine control system. Engine's basic input is air and fuel, output is mechanical driving force
and emission of exhaust gas.
Sensors measure physical variables generated by engine, and the measurements are sent to controllers, ECM as
electric signals after processed by signal processors. Controllers decide various controlling variables and driving
condition required for engine operation, and then generate electric output signal for operating actuators.
Typically engine control requires measuring variables, such as air flow rate, intake manifold and barometric
pressure, coolant and intake air temperature, crank and cam angle, rotational speed, oxygen density in exhaust
gas, throttle angle, presence of Knocking, etc. <Table 1> shows sensors typically used for engine control and
their operating principle.
Therrmistor
-40~120C
(general purpose) -50~130C Coolant temp., Air temp., Room temp.
(coolant temp.)
(MnCoNi type)
Resistance variation by temp.
Thermistor
-40~900C
Temp (high temp.) 600~1000C Catalyzer temp.
(catalyzer temp.)
(Al203, rO2 type)
Resistance-temp.s polar ON, OFF at any Coolant temp., Coolant level, Chock
PTC
characteristic temp. between -40~900C burner
Pressure Semiconductor type Piezo resistance effect 100~780 Torr -40~120C Intake air pressure, Atmospheric
(intake air pressure) pressure
Capacity variation by diaphragm 500~780 Torr (idle mileage control,
Static capacity type
position change (atmospheric ignition timing control, etc)
Electronic generation pressure) engine oil pressure,
Magnet projection+Pick-up coil brake oil pressure
type
Magnetic resistance Two way feature of magnetic
Crank angle, Throttle angle
type resistance type effect
(ignition timing control, EGR
Rotation 0~360C -40~120C
Hall element type Semiconductors Hall effect control, etc),
Engine rpm, Car speed
Wiegand type Wiegand effect
Slit+Light emitint, receiving
Optical type
element
Vane Type Fluid pressure and Vane rotation
Intake air rate
Air flow Karman Vortexs occurance 3
Karman Vortex 0.1~10 m /min -40~120C (idle mileage control, ignition timing
rate frequency
control, etc)
Hot Wire Type Quenching effect by fluid
2. Pressure Sensor
<Table 2> shows input variables used for engine control. Initially they were usually used for intake manifold
pressure, engine oil pressure, etc.
That is, intake manifold pressure is used for indirectly calculating intake air rate for idle mileage control. Earlier
ignition systems used vacuum pressure around throttle valve to measure ignition timing angle. However
requirement for improved engine emission control, fuel mileage and output performance has measured various
input variables used for engine control, and consequently various input sensors are developed and being used.
Fig. 2 is outline of intake system simply. Intake manifold is the route through that air and air/fuel mixture are
inhaled to cylinder. At that time engine works as a pump that draws air into intake manifold.
When engine is not operating, air will not flow, and then intake manifold pressure will be same as atmospheric
pressure. When engine operates, throttle valve located in intake manifold will partly interrupt air flow. Then
pressure in intake manifold will decrease getting lower than atmospheric pressure to generate partly vacuum in
intake manifold. If engine were a perfect air pump and throttle valve is close, then intake manifold pressure will be
absolute zero pressure, say perfect vacuum. However an actual engine cannot be a perfect pump, and perfect
vacuum is not available, intake manifold's absolute pressure is a little above zero. On the contrary when throttle
valve is wide open, intake manifold pressure will be approx. atmospheric pressure. As described above, intake
manifold's absolute pressure will vary from relatively low value to just a little lower value than atmospheric pressure
during engine operation.
Let's observe pressure variation in intake manifold when throttle valve position is constant. Intake manifold pressure
fluctuates rapidly by consecutive suction of air by cylinders. Each cylinder sucks air when intake valves open and piston
drops from TDC, and the intake manifold pressure will decrease. Air intake of this cylinder will be ended upon closure of
intake valve, and intake manifold pressure will continue to rise until next cylinder begins to take air in. This process will be
repeated to fluctuate intake manifold pressure between each cylinder's cycle, and pumping will be done from one
cylinder to another. Each cylinder's air intake action will occur once per two revolution of crank axis. When N cylinders
rotate, intake manifold's pressure fluctuation frequency may be expressed in fig. 3:
N RPM
fp = .........(1)
120
Actual engine control system requires average pressure in intake manifold, and torque generated at constant
engine rpm will be approximately proportional to average value of intake manifold pressure. To say instantly
changing pressure in intake manifold is not used for engine control, and then average value after filtering
fluctuation components will be used. Engine control system has MAP sensor that measures absolute pressure in
intake manifold.
2) Barometric Pressure
Barometric pressure is used as indicator of air density. When altitude rises, air density will decrease to reduce air
intake rate. Therefore required air intake rate in order to maintain constant idle mileage will decrease as altitude
rises. Similarly ignition timing shall be adjusted depending on air density, and is used for some cars to correct EGR
valve's operation and idling speed adjustment. As described Barometric pressure measurement is required to
compensate air density variation by altitude or weather, and performed by BPS(Barometric Pressure Sensor).
Recent trend is using a sensor built in ECM rather than separated BPS.
(1) Classification
Pressure sensors may be classified by installation method as direct attachment on surge tank type an hose
connection type, and by purpose as MAP sensor, Map & IAT sensor, fuel tank pressure sensor, barometric
pressure sensor, booster pressure sensor, EGR monitoring sensor, etc.
Inside MAP sensor, a pressure sensor cell made by semiconductor process is located. By outside packaging,
sensor cell may be classified into can type and plastic mold type; by semiconductor process into bi-polar type and
MOS type; and by feature adjusting method into laser trimming type and digital trimming type.
Sensor chip made as integrated structure of pressure detecting part(diaphragm) and signal processing part, is
located on glass block and connected with packing terminal via AI-wire bonding. Pressure approval is given to
diaphragm front side or back side, and at the other side exist vacuum.
Sensor chip's basic structure may be characterized by integration of diaphragm and signal processing part, and
four diffused resistors using piezo resistance effect make wheatstone bridge on diaphragm.
Diaphragm
Signal processing
part
Sensor chip is approx. 3~4mm, and thickness of diaphragm is approx. 25~40um. Diaphragm is manufactured by
ultra-precision manufacturing technology called micro electro mechanical system(MEMS), in the forms of circle,
square, and rectangular.
Wheatstone bridge formed on diaphragm using piezo resistance effect, generates voltage output by resistance
components variation depending on approved pressure.
Piezo resistance effect generates resistance components when conductor's area or length varies, and provides
linear resistance variation by physical variables applicable. As to silicon resistors, stress makes distortion at silicon
lattice, and then change edge status of conductive band or pendulusive band, so that resulting change of carrier
number and movability varies crystal's electric resistance.
When voltage is approved, compressive force will be applied to two resistors and tensile force to the other two
resistors, changing resistance components in order to generate output voltage gap.
4) MAP Sensor
Fig. 10 represents example of MAP sensor circuit and terminal configuration. Terminal 1 is sensor's input voltage
with 5, terminal 2 is sensor's output terminal, and terminal 3 is for grounding.
Digital volt-meter is used to measure sensor's supply voltage. With ignition switch on, measure output voltage at
terminal1 and decide if there is specified input voltage (5V). Sensor output signal can be measured at terminal 2
Then with ignition switch on (not starting up) output voltage shall be approx. 3.9~4.1V, and during idling output
voltage shall be approx. 0.8~1.6V. Fig. 11 illustrates measuring sensor output voltage using digital volt-meter. In
addition connector's connection, and break and short at supply side and ground side.
In case engine goes off sometimes, crank engine and shake MAP sensor harness. Then if engine goes off, it may
be decided as connector's poor contact. If output value goes outside specified value with ignition switch on (no
cranking), MAP sensor or ECM may be faulty. If MAP sensor output voltage is outside specified value but engine
still idles, the following defects other than MAP sensor it self's fault shall be checked. To say, poor connection
between surge tank and hose, imperfect combustion inside cylinder, air leak at intake manifold, etc.
Fig. 12 illustrates example of MAP sensor's output waveform measurement during idling. During idling, if throttle
opening does not change, MAP sensor output voltage will be constant. On the other hand, if throttle opening
changes, MAP sensor output voltage will vary accordingly. The sensor output voltage is low in case of low load of
engine, and then generates high vacuum pressure in intake manifold. In case of high engine load, high output
voltage will be generated and consequently low vacuum pressure in intake manifold. Fig. 12 part A indicates part
of high absolute pressure in intake manifold, and represents low vacuum pressure. Part B indicates that absolute
pressure in intake manifold is rising as throttle valve opens. Part C indicates low output voltage representing low
absolute pressure in intake manifold and high vacuum pressure.
3. Temperature Sensor
1) Outline
Temperature sensors used for engine control include coolant temperature sensor, intake air temperature sensor,
and oil temperature sensor. Most of them are NTC thermister type sensors. As to NTC thermister's output
characteristic, resistance decreases with increasing temperature as illustrated on fig. 13 The measuring
temperature range and characteristic vary depending on constituting substances of thermister.
Fig. 14 represents coolant temperature sensor, fig. 15 represents intake air temperature sensor, and fig. 16
represents cross section of temperature sensor. Coolant temperature sensor is installed for thermister part to
contact with flowing coolant at cylinder block water jacket. Intake air temperature sensor is installed at surge
tank(Delta 2.5 & 2.7) , with the sensor's thermister part contacting with intake air. As these two sensors(IAT &
MAP) are installed at the same part and have functionally associated with each other, they are sometimes
integrated together and installed as a part.
ECU provides 5V supply voltage to sensor part via internal resistance. Then on the basis of sensor resistance
value, signal voltage will rise with lower temperature and drop with higher temperature. ECU detects this voltage
value for calculating temperature.
Fig. 19 illustrates intake air temperature circuit and terminal. Input voltage of 5V is provided to terminal B and
resistance R is installed inside ECM.
When using volt-meter, turn on terminal ignition switch and measure the voltage, and then compare with specified
value. As NTC thermister type is used, higher temperature will reduce output voltage. Otherwise disconnect
connector and check if supply voltage of 5V is operating normally at harness side. In addition check for circuit
break and short.
0 3.3~3.7 V
20 2.4~2.8 V
Ignition switch on
40 1.6~2.0 V
80 0.5~0.9 V
Fig. 21 illustrates output waveform of the sensor using oscilloscope. Oscilloscope waveform is used to observe
output signal variation by time for checking instant circuit break and short.
Fig. 21 part A illustrates the period of low temperature, and part B indicates output voltage decreases with higher
temperature. Part C represents high of intake air temperature. As intake air temperature does not show
significant fluctuation in a short period, it is required to check the waveform for some extended period. Fig. 22
represents engine testing equipment's intake air temperature sensor output at room temperature using
oscilloscope.
(3) Troubleshooting
For troubleshooting of intake temperature sensor, resistance value and output voltage change by temperature
variation are used for diagnosis. Connector connection and break and short shall be checked as well. For
checking a separate part, use similar device generating hot air(ex. Hair dryer, etc), to measure resistance value
and output voltage change by temperature variation. Then if resistance value does not change by temperature
variation, it will indicate sensor failure. Replace the sensor.
Fig. 23 illustrates coolant temperature sensor circuit and terminal. Terminal 1 is for grounding and terminal 2 is fer
output signal. In addition at ECM side of terminal 2 is a built-in resistance to provide sensor's supply power.
In order to achieve optimum idle mileage control for a electronically controlled fuel injection system, accurate
measurement of intake air is required. AFS(air flow sensor) measures intake rate of air that is filtered by air cleaner,
and one of the most important components of EMS.
B. Vane Type
Air mass Detecting Type
(1) K / V Type
Fig. 24 K / V AFS
Control circuit
Protection cap
Control circuit
Barometric pressure sensor
Iiybr id ic
Bluffbody
Stabilization plate
Karmain
vortex Ultransonic recevier
Main pass
Bypass
Ultrasonic
trasmitter
Air temperature sensor
B. Ultrasonic Transmitter
When air flows through main route, ultrasonic wave sent from ultrasonic transmitter, will pass through
swirl to the receiver. Then the frequency of ultrasonic wave will be modulated periodically by the
generated swirl.
C. Control Circuit
Control circuit detects potential difference of ultrasonic wave that passed through K / V, and generates
electrical pulse signal that is proportional to air flow speed, out of the wave form passed through filter.
The circuit consists of hybrid IC.
D. Thermistor Sensor
K / V AFS measures air temperature at AFS inlet in order to compensate intake air density, using air
volume detecting type.
Measuring Principle(Swirl Detecting Type)
When installing triangular prism(swirling pillar) in fluid flow using K / V phenomenon, asymmetrical and
regular swirl occurs behind the prism. The sensor detects the swirl using ultrasonic wave and transform it to
electrical pulse signal. Then relation between detected frequency and air flow speed may be represented
as the below.
u
f = St
d
When actual air flow is of Reynolds number 102 ~ 105, Strouhal number is almost constant at approx. 0.2.
Therefore if the route is designed to provide engine's air intake rate with in the said Reynolds number range, then
Strouhal number will be almost constant through measurement range, and it will be allowed to decide air flow rate
by detecting K / V's generated frequency of the said formula. Therefore intake air volume will be [air flow speed u]
x [air route's effective area]. Air flow rate measurement of K / V type depends on volume flow rate, and then
requires compensation against mass variation by air temperature and pressure using intake air temperature
sensor and barometric pressure sensor.
A. Output Signal
Fig. 28 illustrates that K / V AFS control unit's output signal is digital signal of spheric wave. Higher air
intake rate generates more swirls raising output signal frequency. Control unit calculates air intake rate
using the output signal.
B. Output Features by Engine Condition
- In idling : F>28HZ
- At pull load: F<2Khz
- In dynamic range: approx. 70 times
Fig. 28 Frequency Variation and Output Features by Air Flow Rate Change
Mirror type relies on the principle that electrical signal will be generated when light emitted from LED that is
located at mirror's top side is reflected by mirror and then emitted to photo transistor. When mirror vibrates
by pressure change, light intensity will change according to reflecting angle, then it will be detected as
current variation that then will be converted to pulse signal. Therefore we can get electric pulse signal
corresponding to swirl occurrence.
Movable vane type uses the principle that movable vane's angle will correspond to air intake, rate when intake air
flows through the route and movable vane's kinetic force and return spring's recovery force are stabilized with
each other. The opening angle is detected by potentiometer that is linked to movable vane.
Configuration
As illustrated on fig. 31, compensation plate and dampening chamber stabilizes vane motion against rapid
change of air intake rate and air pulsation. Idle-mixture adjusting screw is installed at by-pass route, and used to
adjust the feature at low air rate. The screw adjusts idling mileage that varies by each engine and system, within
specified objective range by adjusting by-pass route area and consequently changing AFS output.
Measuring Principle
Movable vane type AFS relies on the principle that measuring plate(vane) is pushed open by pressure gap
generated by flow of air sucked into engine. On turning axis of vane is located return spring of spiral shape.
Vane stops at the position where air flow force to open vane and recovery force of return spring are
balanced. Potentiometer detects the position to obtain voltage value corresponding to intake air rate.
Output Characteristic
Vane type AFS ultimately outputs voltage ratio variation from potentiometer that is located at the same axis
with vane. The output and air flow rate Q have the following inter-relation.
Us C
=
Ub Q
Potentiometer's output voltage Us varies simultaneously with battery voltage change. Then if voltage ratio is
used for output signal, Us signal will vary in proportion to supply voltage Ub variation approved by
potentiometer, and the AFS signal Us/Ub will be constant. Therefore ECM will use it for calculating air flow
rate.
Configuration
1. Hybrid Assy
2. Cover
3. Metal Case
4. Inner Tube with Hot Wire
5. Housing
6. Grid
7. Clamp Ring
The sensor consists of air temperature compensation resistance that detects intake air temperature, circuit
part that generates heat corresponding to heat generation, control circuit part for measurement, and
housing.
Measuring Principle
When heating object is placed in the air the object is cooled by emitting heat toward air, and if there is higher air
flow around the object heat loss will increase by air. Hot wire type sensors use the said phenomenon of heat
transfer between a hot object and air. This type is detecting air mass and not affected by air density variation.
Therefore ECU in principle is not required to compensate against temperature or pressure. The below fig. 35
outlines air flow inlet part and circuit configuration.
Output Characteristic
Output voltage at both ends of standard resistance, varies significantly by current, and higher air intake rate
raises signal voltage.
Configuration
Hot film type depends on the same principle of heat transfer as hot wire type, but has some improvement of
demerits from hot wire type as follows:
- Simplified by-pass design by reducing sensor wire length. Better connection with throttle body.
- Cost saving
- Eliminates wire dirt build-up(foreign material build-up on sensing resistance surface)
- Faster response
In addition it may be classified by ceramic type HFS installed in air route, say housing.
Hybrid assy
O-ring
Housing assy
Hybrid IC
Sensor element
Sensor element consists of air temperature compensation resistance(Rt) for compensating output
characteristic(Rh), heating resistance, and sensing resistance(Rs). Flow grid is installed to stabilize intake
air flow at housing's air inlet part.
Measuring Principle
In principle the measurement basically relies on heat transfer system. Sensor resistance(Rs) that constitute
wheatstone bridge circuit, is heated by rear-side heating resistance(Rh) to be constantly 170 higher than
ambient air temperature. If air flow increases, sensing resistance's temperature will decrease and the
resistance value will drop. Then wheatstone bridge circuit will be unbalanced to generate heating current,
and then heated heating resistance will raise sensing resistance's temperature and resistance value to
achieve balance. The voltage value generated by heating resistance and heating current will be
proportional to air flow rate and consequently possible to measure. Air temperature compensation
resistance(Rt) is designed to compensate resistance variation of sensor output characteristic value by Rh
and Rs variation depending on ambient air temperature.
Output Characteristic
Output voltage at both ends of standard resistance, varies significantly by current, and higher air intake rate
raises signal voltage.
MAF
TPS
Output Voltage [V]
Configuration
This type HFM has plug-in sensor integrated at the same air route part as air cleaner housing, on used
as plug-in sensor module integrated onto cylinder housing as the above picture. In addition various size
cylinder housings are designed depending on required air flow rate for combustion engines. Then this
type HFM may be said to have basically same configuration with conventional HFM type. However
some difference exists for sensor element that senses air flow rate and basic measuring principle.
Sensor element consists of thin silicon diaphragm manufactured using MEMS(micro electro mechanical
system) technology, and heating resistance and a number of temperature sensors which are installed
on the diaphragm. Sensor's signal processing circuit is configured on ceramic board(hybrid IC) located
inside plug-in sensor housing, and includes sensor dement and Au-wire bonding. In addition EPROM
type is used to adjust output characteristic against air flow value, and the circuit is filled with Si-Gel to
protect the circuit. HFM5f includes separate intake air temperature sensor installed on plug in sensor
housing.
Measuring Principle
The thin diaphragm integrated on sensor element is made by etching technology. On diaphragm, heating
resistance is located at center, and temperature sensors T1 & T2 each at front and rear side of heating zone
at air flowing direction. The two sensors will have same temperature when there is no air flow. However
when air flows, T1 sensor located in front of heating zone will be cooled by heat recirculation. On the
contrary T2 sensor located at rear of heating zone will maintain almost same temperature by air heated
through heating zone. Therefore the two sensors will indicate temperature gap by air flow rate through the
route, and the temperature gap will depend on air flow rate that will pass through sensor element. If reverse
air flow occurs through sensor element, the temperature between T1 and T2 will be reversed, as well.
Therefore detecting the temperature gap will enable detecting possible reverse flow.
Output Characteristic
Reverse flow detecting HFM outputs voltage value by intake air flow rate, and provides reverse flow
detection. The below figure illustrates reverse flow detecting characteristic in pulsation test of hot wire type
and reverse flow detecting HFM devices.
Pressure Sensor
Pressure Sensor detects intake manifold's pressure variation as voltage variation, and connected with
surge tank via rubber hose or directly attached at surge tank. Pressure sensor is constituted of pressure
conversion element and circuit part that processes conversion element's output signal. The sensor's output
is proportional to intake manifold's vacuum pressure.
Intake air temperature sensor detects engine intake air temperature. In case of direct measurement type,
the sensor is installed at air intake hose or AFS. In case of speed density type the sensor may be installed at
surge tank in order to sense intake air temperature at pressure induction part. (MAP with IAT sensor)
This type detects air intake rate by estimating air intake quantity into engine per cycle based on throttle
opening angle and engine rpm, and calculate gasoline injection rate. However air intake rate and the
two measurements have complicated functional correlation, and consequently detecting air quantity is
not easy. Therefore currently no vehicle of this type is at market. Only some systems that take other
type of AFS are using this type as backup mode in case of AFS failure.
3) Sensor Checking
Fig. 45 illustrates hot film type air flow sensor's circuit diagram and terminal configuration. Terminal 1
indicates output signal, terminal 2 is for sensor power supply, and terminal 3 is for grounding. However
terminal configuration may differ by car models. Please refer to relevant service manuals.
Fig. 45 Example of Hot Film Type AFS Circuit and Terminal Configuration
Fig. 46 illustrates Karman Vortex Type air rate sensor's circuit and terminal. The sensor is usually installed
together with intake air temperature sensor and barometric pressure sensor. Therefore it is required to be
careful when finding terminals.
Fig. 46 Example of Karman Vortex Type Air Rate Sensor Circuit Diagram and Terminal Configuration
Fig. 47 Example of Output Voltage's Specified Value for Thermal Film Type Air Rate Sensor
<Table 4> Example of Output Voltage's Specified Value for Thermal Film Type Air Rate Sensor
Output voltage Delta 2.5V 6DOHC engine 0.5 0.5v (At 700 rpm)
When air intake rate does not varies output voltage will be constant. Fig. 49 illustrates measurement using
oscilloscope when air intake rate varies.
Part A indicates wide open state(WOT) of throttle valve to provide maximum acceleration. Part B indicates
flow of idling compensation intake air into intake manifold. Part D represents attenuation by air flap motion.
Usually higher air intake rate raises output voltage.
Fig. 51 Example of Output Waveform of Karman Swirl Type Air Rate Sensor
<Table 5> Example of Specified Output values for Karman Swirl Type Air Rate Sensor
Fig. 52 describes implication of Karman swirl type air flow rate sensor's output waveform. Part A represents
horizontal type of reference voltage. Part B indicates peak-to-peak voltage that is same to reference voltage
value. Part C implies almost grounded condition as horizon. Then voltage drop to ground shall not be more
than 400mV. If the voltage drop is more than 400mV, check the sensor and ECM for poor grounding.
Fig. 52 Karman Swirl Type Air Rate Sensor's Output Waveform Analysis
(3) Troubleshooting
If engine stops intermittently, with engine running shake air flow rate sensor harness. Then if engine goes off,
air flow rate sensor connector connection may be poor.
With ignition switch on(engine does not running), if air flow sensor frequency is not 0Hz, AFS or ECM may
be faulty.
If engine goes on idling though AFS output frequency (or sensor output voltage) is outside specified value,
check the following possible defects except AFS.
A. Air flow in air flow sensor is constrained due to disconnected air intake hose or clogged air filter element.
B. Imperfect combustion in cylinder due to defective ignition plug, spark coil, or injector, or insufficient
compression pressure.
5. Position Sensor
1) Position and Rotation Angle Sensor
Position data for engine control is provided by throttle position sensor(TPS) Motor rotation Sensor(MRS) for some
idling sped control system, EGR valve position sensor for EGR control system, crank position sensor(CKP), cam
shaft position sensor, etc. Those sensors provide engine load condition information, and play important roles for
deciding fuel injection and ignition timing, idling speed adjustment, EGR control, etc. Usually used principles for
detecting position include potentiometer, magnetic resistance, hall effect, electronic induction, optical method, etc.
(1) Potentiometer
Potentiometer is a variable resistor made of resistance wire or resistance object. Fig. 53 illustrates potentiometer's
configuration. Potentiometer consists of power supply terminal and ground terminal, and signal terminal
connected to moving wiper.
Standard input
Ground
Fig. 53 Potentiometer Configuration
Resistance between power supply terminal and ground terminal is entire resistance of potentiometer, and does
not vary. However resistance between signal terminal and ground terminal varies by moving wiper's motion,
generating divided voltage type signal out of constant supply voltage. This potentiometer is used by sensors
including TPS, MRS, EGR valve position sensor, etc, and also used by vane type air flow detector. Fig. 53
provides example of TPS operation. Throttle valve motion moves potentiometer's moving element, and the
moving part's motion generates output voltage at signal terminal. When throttle valve is wide open high voltage
(near to supply voltage) will come out, and when fully closed low voltage(near located between them), output
value will vary between supply voltage and 0V.
(1) Configuration
TPS consists of housing assembly that enables sensor connection and sensor supply voltage approval and
installation of collector ring, potentiometer, and O-ring, Collector ring that is connected with throttle valve axis, and
rotates on potentiometer's variable resistance board, potentiometer - a variable resistor that converts throttle
valve's opening to electrical signal, and O-ring cover.
Housing Assy
Cover
O-Ring Potentiomete
Collector
Collector ring moves in linkage with throttle valve axis, and at end of the ring is connected brush. Brush is linked
with throttle valve in moving on TPS's potentiometer-say a ceramic board on which resistor substance is applied,
so as to provide linear output voltage in proportion with throttle valve opening.
Electrical Characteristic
Rt(total resistance)=R1+R2+R3=2000
R2
= 0.05
Rt
R1 + R 2 R 2
= + 0.895
Rt Rt
R4=850
Up
Input/Output ratio between stoppers: 0.04 0.96
Uv
R1'+R 2
Up = (0 R1' R1)
R1 + R 2 + R 3
Where R1' is resistance value of resistance substance R1 applied on ceramic board, that varies when
brush moves. R1' value varies when brush moves on potentiometer in linkage with throttle valve. Therefore
TPS's output voltage Up varies in proportion to throttle valve opening. Fig TPS's electrical Circuit Diagram
TPS's output characteristic curve is indicated as values corresponding to throttle vale opening. The output value is
represented as Up/Uv in order to avoid output value variation output characteristic is, within 96range, Up/Uv=0.05
at 0and Up/Uv=0.94 at 96. The below fig.58 represents ideal output characteristic.
However actual products are hard to obtain ideal output characteristic due to error occurred during manufacturing
process of each part, assembly process, installing process at actual throttle body. Therefore there are specified
values for trimming error, output characteristic slope error, linear error, etc for each resistance in association with
manufacturing process of potentiometer.
TPS measures throttle valve's rotation angle range of a car. Collector ring brush installed in TPS moves in linkage
with throttle valve side, contacting with resistance film surface that is made by applying resistance substance of
thickness of several microns. When the brush rotates on the resistance film, resistance value will vary to provide
different output values that will be used for engine control. However the sensor actually installed on a car provides
abnormal output characteristic due to various causes that are required to be analyzed and improved. In the sense
of those effort non-contact type of rotation angle measurement is suggested to replace conventional contact type
measurement. Several manufacturers have completed or going developing those type rotation angle measuring
sensors. Different type of non-contact rotation angle measurement are available. Among them those types using
magnet's magnetic field characteristic and hall effect are widely used.
Fig. 59 illustrates throttle position sensor circuit and terminals Terminal 1 is for sensor output signal and
terminal 3 is for sensor supply power input.
Checking Procedure
As TPS is a variable resistor, resistance shall be checked first. Disconnect throttle position sensor connector
and measure resistance value between sensor supply power input terminal and ground terminal, and then
compare it with relevant engine's specified value. As specified values differ by applicable model, you shall
refer to relevant engine's maintenance manual. When using voltage value for checking, with ignition switch
on, check 5V voltage at sensor supply power input terminal. Sensor output voltage during idling is specified
as approx. 0.4V~0.9V. In addition slowly operate throttle valve, and observe output resistance or output
voltage variation. If output signal does not vary or outside specified value, check for circuit-break and short,
and replace throttle valve.
Fig. 60 illustrates output waveform during idling measured using oscilloscope. Using the output waveform,
check for instant circuit-break and short signal variation by time. At fig. 60, part A, the output signal indicates
instant short to ground or intermittent circuit-break of potentiometer's resistance. Part B implies throttle
valve's WOT and the highest voltage. Part C represents that output voltage is increasing and throttle valve
is opening. Part D shows that output voltage is decreasing and throttle valve is closing. Part E implies that
throttle valve is closed with minimum voltage. Part F indicates throttle valve is completely closed with ignition
switch on DC offset voltage.
Failure Symptom
3) Hall Sensor
(1) Outline
Hall sensor depends on hall effect and widely used for CKP sensors and CMP sensors.
Gap
Hall Voltage
Fig. 61 illustrates hall effect, hall element is made of small, thin and plain semiconductor substance. When
vertically installing conductor between two permanent magnet, and supplying power to the conductor, electrons in
the conductor will be vertically deflected against supply current and magnets, and then one side will have surplus
electrons and the other side will be short of electrons generating potential difference between two ends. It is called
Hall effect. The generated voltage is proportional to current and intensity of magnetic field, and then if the current is
constant the output will be proportional magnetic field's intensity. However the voltage is not strong enough, and
then boosted before being used.
The Hall sensor is similar to magnetic resistance type sensor. However magnetic resistance type sensor
generates output even though engine is not operating and on the contrary Hall sensor does not have the same
problem. CMP sensor is one of hall sensors, as it relies on Hall effect.
Fig. 62 illustrates cam shaft position sensor circuit and terminal configuration. Terminal 1 is for grounding,
terminals 2 is for output signal, and terminal 3 is for sensor supply power input.
Fig. 62 Example of Cam Shaft Position Sensor Circuit and Terminal Configuration and Wire
Checking Procedure
If cam shaft position sensor is poor, consecutive injection will not occur correctly. Melco system's sensor
failure will make engine start-up literally impossible. If Cam shaft position sensors of Bosch or Siemens
systems are failed, engine may start up. However consecutive injection will not be correct and emission and
mileage in cold start-up may be affected.
For cam shaft position checking, check power supply at terminal 3 using a digital volt-meter. In addition
check connectors for connection, break and short. Waveform may be measured using oscilloscope. Fig.
63 provides example of output waveform of Hall sensor type cam shaft position sensor during idling.
Failure Symptom
The sensor consists of sensor part that includes magnets and soft iron core winded by coil and toothed wheel that
is designed to rotate in linkage with crankshaft. Toothed wheel has 58 teeth and two tooth gaps that is used for
identifying cylinder No.1. Therefore are revolution of toothed wheel make magnetic inductive type crank angel
sensor generate 58 signals.
When crankshaft rotates target wheel linked with crankshaft will rotate together, and then air gap between
inductive CKP sensor wheel teeth varies periodically, that changes magnetism generated by permanent magnets.
Then the magnetism variation will generate AC inductive electromotive force in soft iron core coil. The AC power
will have lower amplitude when toothed wheel revolution is low and higher amplitude when toothed wheel
revolution is high. When the sensor is at the opposite side of reference air gaps that have interval corresponding to
two teeth, the AC power amplitude will rise up to provide detection of cylinder No. 1.
CKP sensor generates a AC pulse per each tooth of toothed wheel, and consequently during one revolution of
crankshaft, 58 AC pulses will be sent to ECM, that will then read the pulse signal to detect crank shaft angle.
(1) Outline
The below figure provides an example of optical type CKP sensor, that consists of LED, photodiode and slit. Light
emitted from LED is detected by photodiode through slit.
Then if slit rotates, the light will be interrupted and consequently photodiode will be unable to generate output
signal. The sensor output characteristic is illustrated on fig. 68 and the sensor outputs digital signal.
Checking Procedure
If abnormal shock is felt during running or engine stops suddenly during idling, shake CKP sensor harness.
If engine stops, check for poor contact.
In case of electronically inductive CKP sensor, if tachometer indicates "0" rpm during cranking, check CKP
sensor and ignition system for defect. If engine is cranked, tachometer indicates "0" rpm, and engine does
not start up, check ignition coil ECM's power TR for defect.
In case of Optical CKP sensor, if CKP sensor outputs pulse signal with ignition switch "on" (no start-up),
check CKP sensor and ECM for defect. If engine does not start up and sensor output signal during cranking
is "0" rpm, check CKP sensor and timing belt for defect. If CKP sensor rpm is out side specified value and
idling is possible, check coolant temperature sensor for failure.
Digital circuit tester is used to check sensor for circuit-break and short, and connector for contact condition.
As CKP sensor provides periodic signal, it is required to check output waveform using oscilloscope. Fig. 71
illustrates measurement of electronically inductive CKP sensor at engine rev of 2000rpm. Fig. 72 illustrates
output waveform measurement in case of idling (780rpm).
The below figure indicates output voltage varies by engine rpm. To say max. voltage is approx. 6V at
2000rpm and approx. 2.7V during idling.
Missing
tooth
1mSec/Div 5Volts/Div
Missing
tooth
2mSec/Div 5Volts/Div
The frequency is approx. 2kHz at 2000rpm. If tonewheel's protrusions are 60, engine rpm may be
calculated using the below formula.
As frequency(f) is reverse to period(T), engine revolution(N: rpm) is:
1
Engine rpm(N) = .......... ................(1 13)
T No. of protrusion
Missing tooth on fig. 72 is the part where protrusion is eliminated to provide reference point.
Fig. 73 illustrates Electronically Induction CKP Sensor Output Waveform analysis.
Fig. 73, part A indicates maximum voltage, that each waveform represents the same value. If a value is
lower than others, it will imply that tonewheel protrusion is broken or bent. Part B indicates minimum
voltage, and the same principle as part A may be applicable. In addition gaps between tonewheel's
protrusions and sensor's detecting part shall be constant. If the gap is outside specified value, output
voltage will vary.
Fig. 74 illustrates optical CKP sensor's output waveform. Optical CKP sensor generates output
waveform of digital pulse type as illustrated. Fig. 74, part A indicates reference voltage represented as a
constant horizon, and part B implies the moment when output signal is off, represented as vertical line.
Part C indicates peak-to-peak voltage, same as reference voltage. Part D shows almost grounded state,
expressed as constant horizon. Higher engine rpm raises frequency.
Failure Symptom
Lead switch type sensor generates 4 pulse signals per a revolution of output gear. Lead switch interrupts 5V
power supply from ECM to convert generated speed signal to pulse signal. Then ECM receives the pulse signal,
that will be used for idling speed adjustment.
Hall sensor type finds whether car is in idling or running. When current flows it receives 0.5V, when Hall sensor
does not operates it receives 12V signal, to detect car speed. To say it has the role to detect load.
In particular, in case of A/T cars, engine may go off when the car stops if car speed sensor is faulty, and
therefore more careful checking is therefore more careful checking is required. In addition, Hall sensor
types may have different pulse number by model, and therefore must check whether the same
specification is used.
56 Chonan Technical Service Training Center
Sensor
1) Checking Procedure
If there is a circuit-break or short at speed sensor wiring, engine may go off when decelerating the car to stop.
Therefore connector connection and wiring's short circuit or circuit break must be checked. For Speed sensors of
lead-switch type or Hall effect, generate digital pulse type signal as illustrated on fig. 87. Therefore it is required to
analyze signal using oscilloscope. To say, check if frequency, period, and specified voltage value occur normally.
Check if frequency rises in proportion to car speed variation. Check if input voltage and grounding are maintained
normally at on and off condition. Speed sensor input voltage is 5V for lead-switch type and 12V for Hall sensor
type.
Fig. 76-1 illustrates analysis of speed sensor output waveform of digital pulse type. Part A indicates reference
voltage and represented as constant horizon. Part B indicates voltage variation state, and represented as vertical
line. Part C indicates peak-to-peak voltage, same as reference voltage. And part D shows almost grounded state,
expressed as constant horizon. AS car speed rises, speed sensor output frequency goes up. Voltage drop at
ground shall be less than 400mV. If not check speed sensor and ECM for defective grounding.
2) Failure Symptom
7. Oxygen Sensor
1). Outline
As air pollution has become a social issue, vehicle emission control has been enhanced. Auto makers have been
developing various technologies. Among them, post-treatment of exhaust gas technology using 3 element
catalyzer is the most widely used one. 3 element catalyzer simultaneously perform oxidation of HC, CO and
deoxidation of Nox to restrain generation of hazardous emission gas. Fig. 77 illustrates purifying efficiency of 3
element catalyzer depending on air/fuel mixture ratio.
Air ratio
3 element catalyzer demonstrated that purifying efficiency of HC, CO and Nox is highest around theoretical air/fuel
ratio. At thicker ratio than theoretical ratio, CO and HC emission is higher, and at thinner ratio than theoretical ratio
Nox emission is higher. Therefore it is required to control that combustion to occur at theoretical air/fuel ratio, for
effectual operation of 3 element catalyzer. It is called air/fuel ratio control or Lamda control. For air/fuel ratio control,
it is required check whether combustion is occur ring at theoretical ratio, and oxygen sensor is installed for this
purpose. Oxygen sensor is a chemical voltage generation device that generates voltage depending oxygen
concentration in emission gas. If oxygen concentration is higher in emission gas(thinner combustion), and
consequently.
Oxygen concentration gap with ambient air, is lower, then lower voltage will be generated.
On the other hand, if oxygen concentration is low(thicker combustion), and oxygen concentration gap with
ambient air is higher, then higher voltage will be generated. In particularly the trend varies rapidly around
theoretical ratio, and consequently oxygen sensor provides advantageous control of air/fuel ratio.
Typically engine control system's oxygen sensor shall have the below characteristic:
Fig. 78 illustrates ZrO2 oxygen sensor configuration. ZrO2 oxygen sensor is made by adding a little
yttrium(Y203) to ZrO2, and then forming it to test tube to make element, and finally coating platinum on both
sides of element. Sensor's inner side contacts with ambient air and the outer side contacts with emission
gas. ZrO2 element has high resistance and non-conductive at low temperature. At high temperature oxygen
concentration gap will be high between inner and outer side, and only oxygen ions will pass through the
element generating electromotive force.
Fig. 79 illustrates ZrO2 oxygen sensor Operation principle. Each oxygen ion has 2 surplus electrons and
consequently negative polarity. Therefore oxygen ions are attracted by ZrO2, and pulled toward inside of platinum
pole-ZrO2 surface.
Sensor's air contacting part has electrically negative polarity against emission gas, and then electric field
exist between ZrO2 substances, resultantly generating potential gap. The potential gap is proportional to
emission gas oxygen concentration and sensor temperature. Typically oxygen quantity existing in emission
is expressed as oxygen's partial pressure. The partial pressure is defined as oxygen's partial
pressure-to-emission gas pressure-ratio. In case of thicker mixture, oxygen's partial pressure ranges
1016~1032 of air pressure, and in case of thinner mixture approx. 102.
Fig. 80 illustrates oxygen sensor's output characteristic by air fuel ratio. For thicker mixture oxygen
concentration in emission gas is low with higher concentration gap resulting to higher potential gap. For
thinner mixture oxygen concentration in emission gas is high with low concentration gap resulting to lower
potential gap. As the change occurs around theoretical ratio, it is called switching characteristic.
However, in actual combustion process the said change is not high enough. Therefore element's surface is coated
with porous platinum to provide enough concentration gap. Platinum catalyzer's reaction is as follows:
1
CO + O2 + CO2 .......... (1 13)
2
When platinum catalyzer burns thicker mixture residual O2 will almost completely react with Co, and remaining O2 on
platinum surface will be nearly zero, generating higher oxygen concentration gap, and approx. 1V of electromotive
force. In case of thinner mixture, O2 concentration in emission gas is high, and CO concentration is low. Therefore
though co react with O2, oxygen concentration will not decrease significantly, and consequently the low concentration
gap will generate almost no electromotive force. Fig. 81 compares between oxygen sensors with and without
platinum catalyzer. In addition hysterisis occurs when air/fuel ratio changes from thicker to thinner and when changes
from thinner to thicker. Then it will generate different responding characteristic of oxygen sensor between the two
cases. To say required period of time between thicker-to-thinner and thinner-to-thicker is different. Fig. 82 illustrates
voltage change by temperature. Temperature has significant effect on sensor's output characteristic. At temperature
below 300, sensor output varies rapidly by temperature, and hard to use for engine control. Above 300, sensor
generates stable voltage of approx. 900mV for thicker ratio and approx. 100mV for thinner ratio.
Beside temperature has effect on switching time as illustrated on fig. 83. Required time changing from
thicker to thinner ratio or thinner to thicker is approx. 3200ms and approx ms at 800. Therefore
temperature variation may result to switching time of approx. 2:1.
Lack to excessive
Excessive to lack
Time
Fig. 84 illustrates TiO2 oxygen sensor configuration and output characteristic. TiO2 oxygen sensor is made by
installing TiO2 element at the tip of ceramic insulator. In addition platinum and rhodium catalyzers are used for
improving sensor performance at low exhaust gas temperature. TiO2 oxygen sensor relies on electric resistance
variation of electronic conductor-TiO2 responding to ambient partial pressure of oxygen.
This sensor as characterized with rapidly changing resistance at the point of air/fuel ratio.
Kinds
ZrO2 Oxygen Sensor TiO2 Oxygen Sensor
Items
Principle Ion conductivity Electronic conductivity
Output Electromotive force variation Resistance value variation
Detection ZrO2 surface TiO2 inside
Features Separation between exhaust gas and standard gas Insert element in emission gas
Additives Add itrium for stabilization purpose -
idle mileage Easy adjustment Hard to adjust
Endurance Bad Good
Responsibility Bad Good
Price Good Bad
Fig.85 illustrates example of circuit and terminal configuration of an oxygen sensor with built-in heating wire.
Terminal 3 is for heating wire's power supply, and terminal 4 is for heating wire's grounding. Terminal 1 is for
oxygen sensor's output and terminal 2 is for oxygen sensor's grounding.
Fig. 85 Circuit and Terminal configuration of Oxygen Sensor with Built-in Heating Wire
Checking oxygen sensor involves first basic checks, to say connector connection, and wiring's circuit-break
and short, and thereafter analyze waveform of output signal. Fig. 86 is example of oxygen sensors output
waveform. Normally periodic variation between below approx. 200mV and above 600mV. When no
abnormality is found but sensor output voltage is out side specified value, check items related to air/fuel ratio
adjustment. To say, injector defect, air leak through gasket gap, air intake rate sensor defect, intake air
temperature sensor defect, coolant temperature sensor, fuel pressure, etc above 0.5V, it implies thicker
combustion, and then air intake rate sensor defect and injector leak shall be checked. If average output
voltage is below 0.45V it indicates thinner combustion, requiring to check vacuum leak and sensor defect.
In particular ZrO2 oxygen sensor's resistance shall not be checked directly. As the oxygen sensor itself
generates voltage, resistance measurement may damage the sensor. In order to decide whether oxygen
sensor is faulty or oxygen output voltage is abnormal by faulty air/fuel ratio, approve 14V at oxygen sensor
heater part terminal, and wait approx. 1~2minutes and then read sensor output voltage that shall be
10~100mV.
If output voltage is OK, oxygen sensor may be normal, and then proceed to check other parts.
8. Knock Sensor
1) Outline
For engine's efficiency, engines of higher compression ratio are desirable. Higher compression ratio will raise
engine efficiency, but on the other hand probability of knocking will rise too. Normal combustion in engine is
effected by igniting air/fuel mixture with spark and then spreading inflamed flame front.
However rapid combustion by self ignition may locally occur before flame front reaches normally. The abnormal
combustion may generate rapid pressure rise that will vibrates gas in cylinder to generate shocking noise, that is
called knocking. Knocking may be caused by combustion chamber's shape and accumulated substances,
mixture components, intake manifold's shape, fuel quality, air density and engine temperature. In addition ignition
timing is closely related to knocking and too early ignition timing cause knocking. Knocking will burn out spark plug,
and piston, and damage cylinder head gasket, and bearing. So knocking must be avoided.
Engine knock control is used to constrain the knocking. Knock control detects knocking generated in engine and
retard ignition timing.
Then knock sensor is used to detect knocking.
The best way to detect knocking is to use pressure sensor that measures pressure in cylinder, but the
sensor is expensive. Piezo-Ceramic sensor made as an integrated part with spark plug is also effective for
detecting knocking, but the price is high and the endurance is poor, so that the sensor in not used
significantly.
Knock sensor is using piezo electric effect of piezo-ceramic and is the most widely used for detecting
knocking.
When external stress is applied piezo-ceramics such as quartz(SiO2), Darium fitanate(BaTiO3), and
PZT(Pb(Zr.Ti)03), electric charge is generated at both sides of the crystal. It is called piezoelectric effect.
Installing electric at both sides of piezo-ceramics can detect electric charge generated by external stress.
Force
Knock sensor is usually embedded on cylinder block. Oscillation generated by knock and transferred to
cylinder block, will be converted to electric signal using piezoelectric effect type sensor.
Two kinds of knock sensors are used: Oscillation type sensors have the same oscillation characteristic at
knock frequency bank; and non-oscillation type sensor is the opposite.
Resonance point
Output voltage
Non-oscillation type
1. Mass
2. Housing
Output voltage
3. Piezo ceranic
4. Insulator
5. Terminal
Frequency[kHz]
In order to use oscillation type sensor, those products that have oscillation frequency same with engine's
knocking frequency. However each engine has its own specific knocking frequency and the application
is hard enough to avoid being used currently.
Non-oscillation knock sensor is designed to have oscillation frequency higher than engine's knocking
frequency, and products that have same characteristic irrespective to engine models may be applicable,
and then widely used currently. In case applying non-oscillation type knock sensor, band pass filter that
has center frequency same as engine's knocking frequency, is integrated in interface layer inside ECM.
For precise detection of Knocking, it is desirable to install a knock sensor at each cylinder. However it will
accompany higher cost.
Therefore minimum number of knock sensor is used to detect all knocking occurred at each cylinder.
Typically one knock sensor covers for cylinders and two knock sensors are used to cover six cylinders.
Knock sensors shall be installed where interference by noise and temperature effect may be minimized.
For best example of deciding installing position of knock sensor, fig. 91 indicates point "A" between cylinder
No.2 & No.3 for 4V engine.
Fig. 93 illustrates knock sensor circuit and terminal configuration. Terminal 2 is for output signal, and terminal 3 is
for grounding.
ECM
Knock sensor shall be checked for connection contact condition and circuit-break and short.
As the sensor is installed on cylinder block to detect vibration, the sensor shall be checked if installed with
specified tightening torque. In addition, resistance value and electrostatic capacity between terminal 2 & 3
shall be measured and compared with specified values. Fig. 94 illustrates waveform of output signal
measured by oscilloscope when knocking occurs.
PEAK-PEAK
FREQUENCY
Repeat
Test
The failure symptom is hard for drivers to sense particularly. In case of knock sensor failure, ignition timing
will be controlled to be retarded by approx. 10, and then power may be low during acceleration or knocking
may occur at higher load of engine.