VOLVO
CEM-8C20 - Rear fog lamp. Faulty signal
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
5 modelsC30 (2007–2013), C30 Electric (2011–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
What does this fault code mean?
The CEM feeds the rear fog lamps straight from one output. It has registered a power draw on that output that is lower than expected, which may be caused by a break, a short to battery voltage, or a lamp that is faulty or missing.
Possible causes
- The signal wire to the rear fog lamps is short-circuited to battery voltage
- Open circuit in the signal wire to the rear fog lamps
- One or more lamps are faulty or missing
What you can do
- 1Switch on the rear fog lamps. If they stay dark the fault is likely permanent; if they light but the code was stored earlier, it is intermittent
- 2Check that the rear fog bulbs are intact and sit properly in their holders
- 3With the ignition off, use a multimeter to check that the wire to the rear fog lamps is unbroken and has no battery voltage
- 4Look for chafing and pinched spots along the rear cables
- 5If the fault remains, have a workshop with diagnostic equipment check the wiring and the module
Symptoms you may notice2
- The rear fog lamps do not work
- The rear fog lamps stay lit constantly
General guidance for car owners. Diagnosis on the car can point to a different cause.