VOLVO
CEM-8C21 - Rear fog lamp. Signal too low
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?
Although the code is named too low signal, the CEM registers too high a current draw on the output that feeds the rear fog lamps. That points to the signal wire to the fog lamps being shorted to ground.
Possible causes
- The signal wire to the rear fog lamps is short-circuited to ground
What you can do
- 1Turn on the rear fog lamps. If they do not light, the fault is likely permanent; if they light but the code was stored earlier, it is intermittent
- 2Check that the rear fog lamp fuse is intact
- 3With the ignition off and the lamp connector unplugged, use a multimeter to check that the wire has no contact with ground (the body)
- 4Look for chafing and pinched spots along the rear cables, especially where they run through the wiring harness
- 5If the fault returns, have a workshop check the wiring and the module
Symptoms you may notice1
- The rear fog lamps do not work
General guidance for car owners. Diagnosis on the car can point to a different cause.