VOLVO
CEM-1B03 - Main Battery Diode Or 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 fault concerns the main battery diode, the main battery relay or the secondary battery relay in cars with automatic start/stop. The code is also set when the CEM receives too little supply voltage, if the deviation lasts a short while during a restart after an auto stop. Several parts are involved, so tracing it may take some time.
Possible causes
- The main battery relay is stuck in the closed position
- The secondary battery relay is stuck in the open position
- A damaged main battery diode
- A damaged secondary battery relay
- A blown fuse for the secondary battery
- A broken wire to the secondary battery
What you can do
- 1Check that the fuses are intact, especially the fuse for the secondary battery. The instruction book or fuse list shows their locations
- 2Check that the battery is charged and that the terminals and connections are seated and clean
- 3Use a multimeter to check that the wire to the secondary battery 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.