VOLVO
CEM-1B01 - Main Battery Diode, 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 diode is part of the safety function in cars with automatic engine start/stop. It supplies the vehicle's consumers while the starter motor runs when the engine restarts after an auto stop, if the secondary battery cannot supply enough. The code is set when the diode or its function deviates for a while during a hot restart.
Possible causes
- A broken wire between the main battery and the battery diode
- A damaged battery diode
What you can do
- 1Check that the fuses are intact. The instruction book or fuse list shows their locations
- 2Check that the connections at the battery and on the wire to the diode are seated and not corroded
- 3Check that the wire from the battery to the diode is not chafed or pinched. Use a multimeter to check that it 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.