Diagnostic Trouble Code (DTC) Information

Diagnostic trouble code (DTC) information CEM-B139F01

Condition

Note! Only on vehicles with the function automatic start/stop of engine.

The central electronic module (CEM) monitors the main battery relay and its associated functionality. The battery relay is a disconnector that disconnects the vehicle's battery and starter motor circuit from the rest of the vehicle's electrical system during the time that the engine is restarted after an auto-stop. This is to prevent the low voltage, which briefly occurs when the starter motor is started, from propagating to the rest of the vehicle's electrical system.
The diagnostic trouble code is stored if the control module detects:
- The voltage difference between the main battery and Central electronic module (CEM) exceeds 1 V at the same time as the current from the main battery is 0 A when the engine is idling.
- Incorrect value lasts longer than 5 seconds.
The control module's test for the diagnostic trouble code (DTC) starts in the event of:
- Engine running
- The alternator's charging voltage is 1V greater than the start battery's voltage.

Note! The control module can only detect the fault once the test has been started and the diagnostic trouble code (DTC) is stored when the conditions are met.

Substitute value
- None.

Possible source
- Main battery relay jammed in open position.
- Open-circuit on the cable between the main battery and main battery relay.

Fault symptom[s]
- Driving/Automatic start/stop of engine/Does not work
- Idling/Automatic start/stop of engine/Does not work