VOLVO
CEM-B1A7901 - Rear Fog Lamp Circuit. General Failure Information. General electrical failure
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
4 modelsS80 (2007–), V70 (2008–), XC60 (2009–), XC70 (2008–)
Show models by year and engine (4)
What does this fault code mean?
The CEM supplies the rear fog lamps directly from an output. The fault is stored when the supply wire has a break or is short-circuited to earth, and then the rear fog lamps do not work.
Possible causes
- The supply wire is short-circuited to earth
- Open circuit in the supply wire
What you can do
- 1Check that the fuses for the fog lamps are intact
- 2Switch on the fog lamps and see whether the rear lamps light, then clear the fault code and road test
- 3Check the supply wire to the rear fog lamps for breaks, chafing and pinch damage
- 4Use a multimeter to check that the supply wire is continuous between the connector ends and has no contact with earth
- 5If the fault returns, have a workshop with diagnostic equipment fault-trace the control module and the wiring
Symptoms you may notice2
- The rear fog lamps do not work
- A message appears in the display
What the fault can affect3
- The output switches off during the driving cycle in which the fault is detected
- If the fault remains, the output is switched off permanently after 100 driving cycles where the fault was detected
- Erasing the fault codes and starting a new driving cycle resets the output
General guidance for car owners. Diagnosis on the car can point to a different cause.