Cummins ISX15 CM2250 (2010-12) Fault Code: 242 PID: 84 SPN: 84 FMI: 10 Wheel-Based Vehicle Speed Sensor Circuit Tampering Has Been Detected- Abnormal Rate of Change
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 control module (ECM) and converted into a vehicle speed.
The vehicle speed sensor is located in the rear of the vehicle transmission.
Conditions for Running the Diagnostics
The adjustable parameter ?VSS Anti-Tampering? must be enabled.
This diagnostic runs continuously when the vehicle is in motion, if the feature is enabled.
Conditions for Setting the Fault Codes
The ECM detects a tampering event of the vehicle speed signal.
Action Taken When the Fault Code is Active
The ECM illuminates the amber CHECK ENGINE light and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.
The engine speed operating range is limited to the adjustable parameter ?Maximum Engine Speed without VSS?.
Cruise Control, Gear-Down Protection, and Road Speed Governor features will be disabled.
Conditions for Clearing the Fault Code
To validate the repair using a Diagnostic Road Test, utilize a route that incorporates both stop-and-go city driving and steady state highway driving. It may be necessary to load the unit for certain diagnostics in the ECM to run.
To validate the repair using a Chassis Dynamometer Test, utilize a routine that incorporates acceleration and motoring events, steady state highway operation, and load. This will simulate normal driving and allow the diagnostics in the ECM to run.
The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp after the diagnostic runs and passes.
The ?Reset All Faults? command in INSITE? electronic service tool can be used to clear active and inactive faults.
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 the 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.
Reference the appropriate original equipment manufacturer (OEM) wiring diagram when troubleshooting circuits that utilize wiring supplied by the OEM.
For intermittent power supply and data link communication issues with aftertreatment components, it is highly recommended that the OEM power distribution center fuses and relays be thoroughly checked for loose, missing or intermittent connections.
1) OEM harness
2) ECM calibration
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