U0121

U0121

Diagnosis information - CAN

PSM control unit, communication

Diagnostic conditions
The PSM control unit initially tests internal function sequences after wake-up. If they are OK, all diagnosable outputs are then tested and any faults are stored.

PSM control unit wake-up through:
- Event-induced CAN message
- Ignition on

Possible fault causes
- No power supply for PSM control unit
- PSM control unit incorrectly coded
- Short circuit or open circuit in the CAN drive
- PSM control unit faulty (in most cases the cause is not the PSM control unit but incorrect coding.)

Fault effects
- Communication via the CAN drive is no longer possible
- No other control units are able to communicate with the PSM control unit.

Affected contacts on the PSM control unit
Connector [A]:
- 1 power supply - terminal 30
- 4 power supply - terminal 15
- 6 power supply - terminal 30
- 11 CAN drive high
- 15 CAN drive low
- 16 ground supply - terminal 31
- 32 power supply - terminal 30
- 47 ground supply - terminal 31