SPN 84 - FMI 10 (Fault Code 242)

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

Vehicle Speed Sensor Circuit

Fault Code: 242
PID(P), SID(S): P84
SPN: 84
FMI: 10/10
Lamp: Amber

REASON: Signal indicates an intermittent connection or VSS tampering.

EFFECT: Engine speed limited to Maximum Engine Speed without VSS parameter value. Cruise
Control, Gear-Down Protection, and Road Speed Governor will not work.

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 control module (ECM) and converted into a vehicle speed.

Component Location:
The vehicle speed sensor is located in the rear of the vehicle transmission. Refer to the OEM service manual for location.

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 Engine Control Module (ECM) detected a tampering event of the vehicle speed signal.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE lamp 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, perform a key cycle, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins® electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• The "Reset All Faults" command in the recommended Cummins® electronic service tool or equivalent can be used to clear active and inactive faults.

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 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.

Read More:
SPN 632 - FMI 4 (Fault Code 254)
SPN 647 - FMI 4 (Fault Code 245)


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