Vehicle Speed Sensor Circuit Tampering Has Been Detected - Abnormal Rate of Cha...

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FAULT CODE 242

Vehicle Speed Sensor Circuit Tampering Has Been
Detected - Abnormal Rate of Change
Overview

CODE REASON EFFECT

Fault Code: 242 Vehicle Speed Sensor Circuit Engine speed limited to
PID: P084 Tampering Has Been Detected - maximum engine speed
SPN: 84 Abnormal Rate of Change. Invalid or without VSS parameter value.
FMI: 10/10 inappropriate vehicle speed signal. Cruise control, gear-down
LAMP: Amber Signal indicates an intermittent protection, and road speed
SRT: connection or VSS tampering. governor will not work.

Vehicle Speed Sensor Circuit

Circuit Description

The vehicle speed sensor senses the speed of the tailshaft gear on the vehicle's
transmission. This speed signal is then transmitted to the engine electronic control module
(ECM) and converted into a vehicle speed.

Component Location

The vehicle speed sensor is located in the rear of the vehicle transmission.

Shop Talk

Verify that the feature settings for the vehicle speed sensor anti-tampering (Fault Code
242), application type and automatic transmission are set correctly. If any of these are set
incorrectly for your specific vehicle and application, Fault Code 242 could occur
erroneously.

Driving techniques such as driving for extended periods of time in lower gears can log Fault
Code 242. Fault Code 242 can be logged if the driver attempts to defeat the road speed
governor by repeatedly cycling the keyswitch.

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Once the speed signal has been restored the fault code will go inactive once the keyswitch
is on for 30 seconds and the ECM senses zero vehicle and engine speed.

Cautions and Warnings

CAUTION
To reduce the possibility of damaging a new ECM, all other active fault
codes must be investigated prior to replacing the ECM.

CAUTION
To reduce the possibility of pin and harness damage, use the following
test leads when taking a measurement:
Part Number 3822758 - male Deutsch/AMP/Metri-Pack test lead
Part Number 3822917 - female Deutsch/AMP/Metri-Pack test lead.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Verify that the feature settings are
correct.
STEP 1A. Verify that the customer Customer wants Vehicle Speed
wants Vehicle Speed Anti- Sensor Anti-Tampering enabled?
Tampering (Fault Code 242)
enabled.
STEP 1B. Verify that the vehicle The setting in INSITE™ electronic
speed sensor and the setting in service tool matches the speed sensor
INSITE™ electronic service tool type on the vehicle?
match.
STEP 1C. Verify that the Anti- Sensitivity Level is set correctly?
Tampering Sensitivity Level is set
correctly for the application.
STEP 2. Look for signs or evidence of
tampering.
STEP 2A. Inspect the vehicle Tampering, installed incorrectly or
speed sensor. external device present?
STEP 2B. Check for open circuit Less than 10 ohms?
in the OEM harness.
STEP 2C. Check for short circuit More than 100k ohms?
to ground in the OEM harness.
STEP 2D. Check for a pin-to-pin More than 100k ohms?
short circuit in the OEM harness.

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STEP 3. Check the vehicle speed

reporting.
STEP 3A. Use INSITE™ INSITE™ electronic service tool
electronic service tool to monitor readout and the vehicle speedometer
the vehicle speed signal. match?
STEP 3B. Verify the vehicle Vehicle speed is accurate?
speed.
STEP 4. Clear the fault codes.
STEP 4A. Disable the fault codes. Fault Code 242 inactive?
STEP 4B. Clear the inactive fault All fault codes cleared?
codes.

Guided Step 1 - Verify that the feature settings are

correct.

Guided Step 1A - Verify that the customer wants Vehicle Speed Anti-
Tampering (Fault Code 242) enabled.

Action

Verify that the customer wants Vehicle

Speed Sensor Anti-Tampering feature
enabled.

Customer wants Vehicle Speed Sensor Customer wants Vehicle Speed Sensor
Anti-Tampering enabled? Anti-Tampering enabled?
YES NO
No Repair Use INSITE™ electronic service tool,
disable the Vehicle Speed Sensor Anti-
Tampering feature.

Go to 1B Go to 4A

Guided Step 1B - Verify that the vehicle speed sensor and the setting in
INSITE™ electronic service tool match.

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Conditions

z Turn keyswitch ON.

z Connect INSITE™ electronic
service tool.

Action

Use INSITE™ electronic service tool, go

to the Vehicle Speed Source feature
under Adjustments, Features and
Parameters.

z Verify that the Vehicle Speed

Sensor Type parameter setting in
INSITE™ electronic service tool
matches the physical sensor type
on the vehicle.

The setting in INSITE™ electronic The setting in INSITE™ electronic

service tool matches the speed sensor service tool matches the speed sensor
type on the vehicle? type on the vehicle?
YES NO
No Repair Change the setting in the ECM with
INSITE™ electronic service tool to match
the vehicle speed sensor type.

Go to 1C Go to 4A

Guided Step 1C - Verify that the Anti-Tampering Sensitivity Level is set

correctly for the application.

Conditions

z Turn keyswitch ON.

z Connect INSITE™ electronic
service tool.

Action

Verify that the Vehicle Speed Signal

Tampering Sensitivity Level is set
correctly for the application.

z Use INSITE™ electronic service

tool go to the Vehicle Speed
Source feature under Adjustments,

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Features and Parameters.

z Check the ECM setting for Vehicle
Speed Signal Tampering
Sensitivity Level.

Sensitivity Level is set correctly? Sensitivity Level is set correctly?

YES NO
No Repair Use INSITE™ electronic service tool to set
the Vehicle Speed Signal Tampering
Sensitivity Level to the correct value for the
vehicle.

Go to 2A Go to 4A

Guided Step 2 - Look for signs or evidence of tampering.

Guided Step 2A - Inspect the vehicle speed sensor.

Action

Inspect the vehicle speed sensor for the

following:

z Improper mounting of the vehicle

speed sensor
z Vehicle speed sensor improperly
connected to the OEM harness
z Other external device connected in
place of the vehicle speed sensor
z Any evidence that tampering with
the vehicle speed sensor has
taken place.

Tampering, installed incorrectly, or Tampering, installed incorrectly. or

external device present? external device present?
YES NO
Remove the tampering device. No Repair

Install the sensor correctly or remove the

external device.

Go to 4A Go to 2B

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Guided Step 2B - Check for open circuit in the OEM harness.

Conditions

z Turn
keyswitch
OFF.
z Disconnect
the OEM
harness from
the ECM.
z Disconnect
the OEM
harness from
the vehicle
speed
sensor.

Action

Using a
multimeter, check
for an open circuit
in the OEM
harness.

z Measure the
resistance of
the magnetic
vehicle
speed
sensor
SIGNAL (+)
wire between
the OEM
harness
ECM
connector
and the OEM
harness
magnetic
vehicle
speed
sensor
connector.
z Measure the
resistance of
the magnetic
vehicle

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speed
sensor
SIGNAL (-)
wire between
the OEM
harness
ECM
connector
and the OEM
harness
magnetic
vehicle
speed
sensor
connector.

Refer to the wiring

diagram for
connector pin
identification.

For general
resistance
measurement
techniques, refer
to Resistance
Measurements
Using a Multimeter
and Wiring
Diagram,
Procedure 019-
360.

Less than 10 Less than 10 ohms?

ohms?
YES NO
No Repair An open circuit has been detected in the OEM harness.

Repair or replace the OEM harness.

Refer to Procedure 019-071.

Go to 2C Go to 4A

Guided Step 2C - Check for short circuit to ground in the OEM harness.

Conditions

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z Turn
keyswitch
OFF.
z Disconnect
the OEM
harness
connector
from the
ECM.
z Disconnect
the OEM
harness from
the vehicle
speed
sensor.

Action

Check for a short

circuit to ground
on the magnetic
vehicle speed
sensor SIGNAL
(+) and magnetic
vehicle speed
sensor SIGNAL (-)
circuit in the OEM
harness.

z Measure the
resistance
between the
magnetic
vehicle
speed
sensor
SIGNAL (+)
pin at the
ECM
connector to
engine block
ground.
z Measure the
resistance
between the
magnetic
vehicle
speed
sensor
SIGNAL (-)
pin at the
ECM

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connector to
engine block
ground.

Refer to the circuit

diagram or wiring
diagram for
connector pin
identification.

For general
resistance
measurement
techniques, refer
to Resistance
Measurements
Using a Multimeter
and Wiring
Diagram,
Procedure 019-
360.

More than 100k More than 100k ohms?

ohms?
YES NO
No Repair A short circuit has been detected in the OEM harness.

Repair or replace the OEM harness.

Refer to Procedure 019-071.

Go to 2D Go to 3A

Guided Step 2D - Check for a pin to pin short circuit in the OEM harness.

Conditions

z Turn
keyswitch
OFF.
z Disconnect
the OEM
harness from
the ECM.
z Disconnect
the OEM
harness from

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the vehicle
speed
sensor.

Action

Using a
multimeter, check
for a pin-to-pin
short circuit in the
OEM harness.

z Measure the
resistance
and check
for a short
circuit
between the
magnetic
vehicle
speed
sensor
SIGNAL (+)
pin at the
OEM
harness
ECM
connector
and all other
pins in the
connector.
z Measure the
resistance
and check
for a short
circuit
between the
magnetic
vehicle
speed
sensor
SIGNAL (-)
pin at the
OEM
harness
ECM
connector
and all other
pins in the
connector.

Refer to the circuit

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diagram or wiring
diagram for
connector pin
identification.

For general
resistance
measurement
techniques, refer
to Resistance
Measurements
Using a Multimeter
and Wiring
Diagram,
Procedure 019-
360.

More than 100k More than 100k ohms?

ohms?
YES NO
No Repair A short circuit has been detected in the OEM harness.

Repair or replace the OEM harness.

Refer to Procedure 019-071.

Go to 3A Go to 4A

Guided Step 3 - Check the vehicle speed reporting.

Guided Step 3A - Use INSITE™ electronic service tool to monitor the

vehicle speed signal.

Conditions

z Turn keyswitch ON.

z Connect INSITE™ electronic
service tool.

Action

Use INSITE™ to check the vehicle

speed.

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z Verify that the vehicle speed is 0

when the vehicle is stationary and
the engine is running.
z Drive the vehicle or run on a
chassis dynamometer. Compare
the vehicle speed read by
INSITE™ electronic service tool to
the speedometer on the dash.

INSITE™ electronic service tool readout INSITE™ electronic service tool readout
and the vehicle speedometer match? and the vehicle speedometer match?
YES NO
No Repair Verify that the Tire Size, Rear Axle Ratio,
and Tailshaft Gear Teeth parameters are
set correct in the ECM.

Go to 3B Go to 4A

Guided Step 3B - Verify the vehicle speed.

Conditions

z Turn keyswitch ON.

z Connect INSITE™ electronic
service tool.
z Vehicle moving.

Action

Use INSITE™ to verify that the speed

reported is accurate or reasonable for
the current gear.

z (For example: 64 km/h [40 mph] in

top gear is probably inaccurate
data)

Vehicle speed is accurate? Vehicle speed is accurate?

YES NO
No Repair Verify that the Tire Size, Rear Axle Ratio,
and Tailshaft Gear Teeth parameters are
set correct in the ECM.

Go to 4A Go to 4A

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Guided Step 4 - Clear the fault codes.

Guided Step 4A - Disable the fault code.

Conditions

z Connect all components.

z Turn keyswitch ON.
z Engine not running.
z Vehicle not moving.

Action

Disable the fault code.

z With the keyswitch ON and the

vehicle stationary, wait 1 minute.
z Use INSITE™ electronic service
tool, verify that Fault Code 242 is
inactive.

Fault Code 242 inactive? Fault Code 242 inactive?

YES NO
No Repair Return to the troubleshooting steps or
contact your local Cummins Authorized
Repair Location or OEM dealer if all the
steps have been completed and checked a
second time.

Go to 4B Go to 1A

Guided Step 4B - Clear the inactive fault codes.

Conditions

z Connect all components.

z Turn keyswitch ON.
z Connect INSITE™ electronic
service tool.

Action

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Clear the inactive fault codes.

z Use INSITE™ electronic service

tool to erase the inactive fault
codes.

All fault codes cleared? All fault codes cleared?

YES NO
No Repair Troubleshoot any remaining fault codes.

Repair complete Appropriate troubleshooting steps

Last Modified: 30-Jan-2006

Copyright© 2006
Cummins, Inc.
All rights reserved

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