VOLVO
CEM-B101288 - Left Headlamp Control. 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?
This fault concerns the left main headlamp control unit (LHCU), which the central electronic module (CEM) communicates with over the LIN bus. The fault is stored when the bus is shorted to voltage or earth, which affects the headlamp adjustment.
Possible causes
- LIN bus shorted to voltage or earth
- Damaged left main headlamp control unit (LHCU)
What you can do
- 1With the ignition off, check that the wiring to the left headlamp has no chafing, pinching or contact with the body
- 2With the ignition off, use a multimeter to check whether the LIN wire to the left headlamp has contact with earth or voltage
- 3Check that the connectors to the headlamp are secure and not corroded
- 4Clear the fault code and road test to see whether it returns
- 5If the fault remains, have a workshop isolate the bus and check the left headlamp control unit, as this needs diagnostic equipment and sometimes new software
Symptoms you may notice3
- Headlamp side adjustment does not follow the steering wheel correctly, or does not work
- Headlamp height adjustment is wrong or does not work
- Main beam with automatic high beam control does not work
What the fault can affect2
- The light range stays fixed at one constant level
- Side adjustment is locked in the straight-ahead position
General guidance for car owners. Diagnosis on the car can point to a different cause.