VOLVO
CEM-B112E21 - Twilight sensor. General Signal Failures. Signal too low
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 central electronic module (CEM) reads the outside light level from the twilight sensor and uses it to set the brightness of the instrument lighting and the button lighting. The code is set when the signal from the sensor is too weak for the system to trust, and the lighting control may then behave incorrectly.
Possible causes
- Signal wire shorted to ground
- Twilight sensor not working
- Poor contact at the sensor or in the wiring harness
What you can do
- 1Check that the fuses for the lighting and the central electronic module are intact; their locations are in the owner's manual or on the fuse box cover
- 2Check whether the instrument and button lighting works in different light conditions
- 3Check the sensor connector and its wire for chafing, short circuits to ground and loose connections
- 4Read the sensor signal with diagnostic equipment and replace the sensor if it does not respond correctly
Symptoms you may notice1
- Instrument and button lighting does not work
General guidance for car owners. Diagnosis on the car can point to a different cause.