VOLVO
CEM-9F31 - Dimmer. Signal too high
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
5 modelsC30 (2007–2013), C30 Electric (2011–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
What does this fault code mean?
The dimmer, meaning the rheostat for the instrument lighting, sends either too high a signal or no signal at all to the central electronic module (CEM). The fault code is then stored. The fault can cause the instrument lighting to stay on at full brightness or not work at all.
Possible causes
- Rheostat shorted to supply voltage
- Open circuit in the signal wire
- Damaged light switch
What you can do
- 1Turn the dimmer control with the lights on and see whether the instrument lighting changes brightness. If it does not react at all, this suggests a fault that is still present
- 2With the ignition off, check the wire from the rheostat and the connectors to the light switch for chafing, pinching and loose connections
- 3With the ignition off, use a multimeter to check whether the signal wire from the rheostat has voltage to earth; voltage there may mean a short circuit to supply voltage
- 4Remedy any wiring faults that are found and clear the fault code
- 5If the fault remains with the wiring intact, have a workshop replace the light switch
Symptoms you may notice2
- The instrument lighting does not work
- The instrument lighting stays on at full brightness all the time
General guidance for car owners. Diagnosis on the car can point to a different cause.