VOLVO
CEM-3F0B - Reverse gear inhibit. Signal too low
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
4 modelsC30 (2007–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
What does this fault code mean?
This variant applies to the C30, C70, S40 and V50. The CEM checks the reverse gear inhibitor. The fault is set if the circuit is shorted to ground. Reverse gear may then be possible to engage even while the car is rolling forwards.
Possible causes
- The signal cable to the reverse gear inhibitor is shorted to ground
What you can do
- 1With the ignition on, try to engage reverse gear and check whether the inhibitor activates
- 2Check that the connectors at the reverse gear inhibitor are seated and not corroded or chafed
- 3Use a multimeter to check that the signal wire to the inhibitor is not shorted to ground
- 4After the work, clear the code and check that the reverse gear inhibitor works
Symptoms you may notice1
- Reverse gear can be engaged even though the car is rolling forwards
General guidance for car owners. Diagnosis on the car can point to a different cause.