VOLVO
CEM-1B02 - Main Battery Relay, General electrical failure
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 main battery relay is a disconnector that, during a restart after an auto stop, isolates the battery and starter circuit from the other electrics. This stops the brief voltage dip from affecting the rest of the car. The code concerns the relay's function in cars with automatic start/stop and can stop the auto stop from working.
Possible causes
- The main battery relay has stuck in the open position
- A broken wire between the main battery and the relay
What you can do
- 1Check that the fuses are intact. The instruction book or fuse list shows their locations. Replace a blown fuse once
- 2Check that the connections at the battery and at the relay are seated and not corroded
- 3Use a multimeter to check that the wire between the battery and the relay has no break
- 4If you have a diagnostic tool, read the fault codes after a drive with auto stop and see whether they return
- 5After the work, clear the code and drive for a while to see whether auto stop works again
Symptoms you may notice2
- Auto start/stop does not work while driving
- Auto start/stop does not work at idle
General guidance for car owners. Diagnosis on the car can point to a different cause.