VOLVO
CEM-B139F01 - Main Battery Relay. General Failure Information. General electrical failure
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
9 modelsS60 (2011–), S80 (2007–), V40 (2013–), V40 Cross Country (2013–), V60 (2011–), V60 Cross Country (2015–), V70 (2008–), XC60 (2009–), XC70 (2008–)
What does this fault code mean?
This fault code only applies to cars with automatic engine start/stop. During a restart after an auto stop, the main battery relay isolates the battery and starter circuit from the remaining electrics, so the brief voltage dip from the starter does not reach the other systems. The CEM monitors the relay, and the fault is stored when the value is wrong for too long.
Possible causes
- The main battery relay has stuck in the open position
- Open circuit in the wire between the main battery and the main battery relay
- Open circuit in the wire between the main battery relay and the battery main fuse box
What you can do
- 1Check that the fuses are intact, especially those in the battery main fuse box
- 2Check that the main battery is fully charged and that the cables from the battery to the relay are intact and clean
- 3Check the connectors at the battery, at the relay and in the main fuse box: loose or corroded connectors should be cleaned and pressed in
- 4If you have a diagnostic tool, check in live data whether the main battery relay shows an open state when the engine is started
- 5If no fault is found in the wiring, have a workshop check and if needed replace the main battery relay
Symptoms you may notice2
- The automatic start/stop function does not work while driving
- The automatic start/stop function does not work at idle
General guidance for car owners. Diagnosis on the car can point to a different cause.