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FAULT CODE 242

Vehicle Speed Sensor (VSS) Circuit

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Overview

CODE REASON EFFECT
Fault Code: 242
PID: P084
SPN: 84
FMI: 10
LAMP: Yellow
SRT: 00-097		 Invalid or inappropriate vehicle speed signal detected on pins 3 and 7 or pin 7 and ground of the OEM harness connector, indicating an intermittent connection or possible tampering. Engine speed limited to “Maximum Engine Speed without Vehicle Speed Sensor” parameter value until keyswitch is OFF for 5 seconds.

Vehicle Speed Sensor Circuit

Circuit Description

The VSS uses two separate coils of wire to count gear teeth as they pass in front of the sensor. One coil is used by the ECM to sense vehicle speed. The other is sometimes used by the OEM to send a vehicle speed signal to the speedometer. (The use of dual coils can vary with OEM.)

Component Location

The VSS is installed into the transmission tailshaft housing.

 

Shop Talk

  • Verify that the feature settings for “VSS Antitampering (Fault Code 242),” “Application Type,” and “Automatic Transmission” are set correctly. If any of these are set incorrectly, Fault Code 242 could occur erroneously.

NOTE: Driving techniques, such as driving for extended periods of time in lower gears, could 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.
  • Interview the driver to discover what occurred when the fault code was logged. Explain the driver actions that can cause Fault Code 242 to be logged.
  • When deactivating the fault, verify that the vehicle is stopped and the engine is shut down.
  • Verify that the keyswitch has been cycled and has remained ON for 30 seconds after the invalid signal has been corrected. This fault will remain active until the keyswitch is cycled and the ECM sees zero vehicle speed and zero engine speed for 30 seconds.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Verify that the feature settings are set correctly.
STEP 1A. Verify that the customer wants “VSS Antitampering (Fault Code 242)” enabled. Customer wants “VSS Antitampering (Fault Code 242)” enabled
STEP 1B. Verify that “Automatic Transmission” is set correctly for application. “Automatic Transmission” is set correctly
STEP 1C. Verify that “Application Type” is set correctly for application. “Application Type” is set correctly
STEP 2. Look for signs of tampering.
STEP 2A. Inspect the VSS. No signs of tampering detected at or with the vehicle speed sensor
STEP 2B. Inspect the OEM VSS circuit. No signs of tampering detected with the VSS leads or the OEM harness
STEP 2C. Monitor the vehicle speed. Electronic service tool displays correct speed
STEP 2C-1. Verify the vehicle speed.
STEP 3. Clear the fault codes.
STEP 3A. Disable the fault code. Fault Code 242 inactive
STEP 3B. Clear the inactive fault codes. All fault codes cleared

Guided Step 1 – Verify that the feature settings are set correctly.

Guided Step 1A – Verify that the customer wants “VSS Antitampering (Fault Code 242)” enabled.

Action

  • Talk to the owner of the vehicle to see if this feature is required for the application of this vehicle.
OK NOT OK
Customer wants “VSS Antitampering (Fault Code 242)” enabled Adjust the feature setting to its correct value using INSITE™.

Guided Step 1B – Verify that “Automatic Transmission” is set correctly for application.

Action

  • Verify that this feature is activated if an automatic transmission is used, or deactivated if a manual transmission is used, using INSITE™.
OK NOT OK
“Automatic Transmission” is set correctly Adjust the feature setting to its correct value using INSITE™.

Guided Step 1C – Verify that “Application Type” is set correctly for application.

Action

  • Verify that this feature setting is set correctly for the application in which this vehicle is used, using INSITE™.

NOTE: Driving for extended periods of time in lower gears is considered an ON/OFF highway application.
OK NOT OK
“Application Type” is set correctly Adjust the feature setting to its correct value using INSITE™.

Guided Step 2 – Look for signs of tampering.

Guided Step 2A – Inspect the VSS.

Conditions

Turn keyswitch OFF.

Action

  • Improper mounting of the VSS
  • VSS improperly connected to OEM harness
  • Other external device connected in place of VSS
  • Any evidence that tampering with the VSS has taken place.
OK NOT OK
No signs of tampering detected at or with the vehicle speed sensor VSS has been tampered with or is improperly installed or connected

Correctly install and connect the VSS to the OEM harness. Refer to Procedure 019-090 or 019-091.
Remove any tampering device.

Guided Step 2B – Inspect the OEM VSS circuit.

Action

  • Broken, cut, or incorrect routing of the VSS wires
  • Any devices connected in series or parallel with the VSS
  • Any other wires added to the VSS circuit
  • Any evidence that tampering with the VSS circuit has taken place.

NOTE: The variable reluctance (magnetic pickup) style of VSS can not tolerate two loads in the same circuit. Any additional loads between the sensor and conditioning circuit or the control module should be removed. Once the signal has been conditioned, other devices can share the speed signal.
OK NOT OK
No signs of tampering detected with the VSS leads or the OEM harness Repair or replace the OEM harness

  • Repair the OEM harness. Refer to Procedure 019-228.
  • Replace the OEM harness. Refer to Procedure 019-071.

Guided Step 2C – Monitor the vehicle speed.

Conditions

  • Install appropriate electronic service tool, preferably INSITE™.
  • Turn keyswitch ON.

Action

  • Verify that the vehicle speed is zero when the vehicle is stationary and the engine is running.
  • Drive the vehicle or run on a chassis dynamometer. Compare the vehicle speed read by the electronic service tool with the speedometer on the dash.

NOTE: If the dash is an electronic dash that uses the ECM to obtain vehicle speed, perform a road test, and use a stopwatch and road mile markers to determine the true vehicle speed.
OK NOT OK
Electronic service tool displays correct speed Electronic service tool and speedometer do not match

Verify that the VSS parameters are adjusted correctly in the ECM. Check the VSS and the OEM harness in Steps 2A and 2B above. Repair any problems found.

Guided Step 2C-1 – Verify the vehicle speed.

Action

(For example: 40 mph in top gear is probably inaccurate data.)
OK NOT OK
Vehicle speed is accurate for present gear Vehicle speed read by electronic service tool is inaccurate.

Verify VSS parameters are adjusted correctly in the ECM. Check VSS and OEM harness in Steps 2A and 2B above. Repair any problems found.
Fault Code 241

Guided Step 3 – Clear the fault codes.

Guided Step 3A – Disable the fault code.

Conditions

  • Connect all the components.

Action

  • Turn keyswitch OFF.
  • Turn keyswitch ON. (Do not start engine.)

NOTE: Vehicle speed and engine speed must be zero for at least 30 seconds to disable the fault code.
OK NOT OK
Fault Code 242 inactive Return to troubleshooting steps or contact your nearest Cummins Authorized Repair Location if all steps have been completed and checked again.

Guided Step 3B – Clear the inactive fault codes.

Conditions

  • Connect all the components.

Action

  • Erase the inactive fault codes using INSITE™.
OK NOT OK
All fault codes cleared Troubleshooting any remaining active fault codes.
Repair complete
Appropriate troubleshooting chart
Last Modified:  01-Sep-2004
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