VOLVO
CEM-B129A86 - LIN Bus "D". Bus Signal / Message Failures. Signal invalid
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 shares a LIN bus with the wiper motor module (WMM), the rain sensor (RSM) and the battery monitoring sensor (BMS). The fault is stored when messages sent on the bus become corrupt. The fault can affect the automatic start/stop function and the wipers, and
Possible causes
- Contact resistance, oxidation or poor contact in the connector terminals and connections
- Damaged wiper motor module (WMM)
- Damaged battery monitoring sensor (BMS)
- Damaged rain sensor (RSM)
What you can do
- 1Check that the battery is charged and that the fuses are intact
- 2Check the connectors at the wiper motor module, the rain sensor and the battery monitoring sensor: oxidised or loose connectors should be cleaned and pressed in
- 3Check the LIN wire between the units for chafing and pinch damage
- 4Have a workshop with diagnostic equipment establish which unit on the LIN bus is sending incorrect messages
- 5If the fault remains, have a workshop check the rain sensor, the wiper module and the battery monitoring sensor
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.