What does fault code TCM-0078 mean?

Diagnostic fault code details for TCM-0078 (Volvo C30 (2007–2013), Volvo C30 (2007–2013), Volvo C30 (2007–2013)). Repair service at OBD Tuning.

VOLVO

TCM-0078 - P-lock function. Signal too high

System

Transmission Control Module (TCM)

Volvo models this fault code applies to

Applies to the following models:

4 models

C30 (2007–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)

Show models by year and engine (10)

What does this fault code mean?

The gear selector has an electrically controlled lock (shift-lock) that is meant to stop it being moved out of position P by accident. The lock should release when the brake is pressed. The fault means the control module has detected a signal to the lock that is too high, because the cable is short-circuited to voltage. The gear selector may then be hard or impossible to move.

Possible causes

Connector or cable is damaged
Damaged gear selector module (GSM)

What you can do

1With the ignition on and the brake pedal pressed: try to move the gear selector out of P. If it still will not move, the fault is present
2Read off the fault code, clear it and check whether it comes back
3Check the cable to the lock for chafing and for connectors that may have touched a live wire; use a multimeter to check that the cable is not shorted to voltage
4Have a workshop check the connector at the transmission control module and the gear selector module; if no fault is found in the wiring, the gear selector module may need replacing

Symptoms you may notice2

Yellow warning symbol and text message in the display
Gear selector hard or impossible to move

What the fault can affect1

The gear selector cannot be moved out of position P

General guidance for car owners. Diagnosis on the car can point to a different cause.