VOLVO
CEM-U000400 - High Speed CAN Communication Bus (+) Low. General Failure Information. No sub type information
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
2 modelsV40 (2013–), V40 Cross Country (2013–)
Show models by year and engine (2)
What does this fault code mean?
On the V40 one of the high speed CAN wires, the positive wire, is shorted to earth. This disturbs communication between the control modules, so the engine may have trouble starting and driving is affected. The fault most often lies in the high speed network wiring.
Possible causes
- Short circuit between the positive wire of the high speed CAN and earth
What you can do
- 1Note when the faults occur, for example at start or under acceleration. This gives a clue to where the wiring is damaged
- 2Check the high speed network harness for chafing and pinch damage where it moves
- 3Check the connectors on the network for loose connections and corrosion
- 4With a diagnostic tool, read the fault codes from all control modules and see which ones show communication faults
- 5Use a multimeter to check that the wire has no contact with earth or the body along its length
- 6If the engine stalls while driving, avoid long journeys and have a workshop trace the fault promptly
Symptoms you may notice4
- The engine does not start even though the starter turns
- Poor performance and lack of power, especially at start
- The throttle response hesitates, surges or is jerky
- The speedometer and tachometer show wrong readings
General guidance for car owners. Diagnosis on the car can point to a different cause.