VOLVO
CEM-9F20 - Twilight sensor. Short-circuit to supply voltage
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
5 modelsS60 (2001–2009), S80 (1999–2006), V70 (2000–2008), V70 XC / XC70 (2001–2007), XC90 (2003–)
What does this fault code mean?
The twilight sensor gives the central electronic module (CEM) information about the light conditions. This information sets the brightness of the symbols and the instrument lighting. The fault code is stored when the signal wire from the sensor is shorted to battery voltage.
Possible causes
- Signal wire from the twilight sensor shorted to supply voltage
- Damaged twilight sensor
What you can do
- 1Check that the twilight sensor is firmly fitted and not covered or damaged
- 2With the ignition off, check the sensor connector and wiring for chafing, pinching and loose connections
- 3With the ignition off, use a multimeter to check whether the signal wire has voltage to earth. Voltage there points to a short circuit to supply voltage
- 4Remedy the short circuit if it is found, then clear the fault code
- 5If no fault is found in the wiring, the twilight sensor may need replacing; have a workshop do this
Symptoms you may notice1
- The instrument lighting stays on at full brightness all the time
What the fault can affect1
- The control module uses the night brightness setting
General guidance for car owners. Diagnosis on the car can point to a different cause.