VOLVO
CEM-B12C988 - LIN Bus "E". Bus Signal / Message Failures. Bus off
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
2 modelsV40 (2013–), V40 Cross Country (2013–)
Show models by year and engine (2)
What does this fault code mean?
The CEM sends messages to the overhead console (OHC) and the rear reading light (RRL) over the LIN bus, but the messages never reach the bus. The fault is stored when this happens, and the bus has then stopped working. The fault affects the panoramic roof sunshade and the passenger compartment lighting.
Possible causes
- The LIN bus is short-circuited to voltage or earth
- Damaged overhead console (OHC)
- Damaged rear reading light (RRL)
What you can do
- 1Check that the fuses are intact
- 2Note which functions in the roof do not work, as this shows which units are affected
- 3Check the LIN wire for short circuits to voltage or earth and for damage
- 4Use a multimeter to check that the LIN wire is not short-circuited to battery voltage or earth with the connectors disconnected
- 5If the fault remains, have a workshop check the overhead console and the rear reading light, one at a time
Symptoms you may notice2
- The electric sunshade in the panoramic roof does not work
- The lighting in the passenger compartment does not work
General guidance for car owners. Diagnosis on the car can point to a different cause.