CM850 Electronic Control System – FAULT CODE 242

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


Fault Code: 242
PID: P084
SPN: 84
FMI: 10/10
LAMP: Amber

Vehicle Speed Sensor Circuit Tampering Has Been Detected – Abnormal Rate of Change. Invalid or inappropriate vehicle speed signal. Signal indicates an intermittent connection or VSS tampering.

Engine speed limited to maximum engine speed without VSS parameter value. Cruise control, gear-down protection, and road speed 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.

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.

Refer to Troubleshooting Fault Code t05-242

Last Modified:  08-Jul-2010