VOLVO
CEM-B129A88 - LIN Bus "D". 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, the wiper motor module (WMM), the rain sensor (RSM) and the battery monitoring sensor (BMS) share the LIN bus. The fault is stored when messages from the CEM never reach the bus, which means the bus has stopped working. The fault can affect the start/stop function and the wipers.
Possible causes
- Damaged connector terminal
- The LIN bus is short-circuited to voltage or earth
- Damaged wiper motor module (WMM)
- Damaged battery monitoring sensor (BMS)
- Damaged rain sensor (RSM)
What you can do
- 1Check that the battery is in good condition
- 2Check that the connectors at the connected units are secure and undamaged
- 3Check the LIN wire for chafing and signs of a short to voltage or earth
- 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 after this check, have a workshop check the rain sensor, the wiper module and the battery monitoring sensor, one at a time
Symptoms you may notice3
- The automatic start/stop function does not work while driving
- The automatic start/stop function does not work at idle
- Yellow warning symbol and text message in the display
What the fault can affect1
- If the wipers are switched on they run at the lowest speed
General guidance for car owners. Diagnosis on the car can point to a different cause.