P0686

P0686

Diagnosis information - DME (DFI)

Main relay off

NOTE:
- After the ignition is switched off (terminal 15), the DME control unit switches to control unit after-run mode.
- There is no longer any voltage present (0 V) at DME control unit connector contact A34 after the end of after-run.
- A check is made to determine whether the main relay has switched off (voltage less than 4 V at contacts A3 / A5 / A6).

NOTE:
- The after-run period depends on many boundary conditions (e.g. engine temperature for fan operation).
- It is possible to establish whether the DME control unit is currently in after-run mode . To do this, switch on the ignition, connect the PIWIS Tester, establish communication with the DME control unit and then switch the ignition off again. The DME control unit is in after-run mode as long as communication with the tester is maintained.

Diagnostic conditions
- Vehicle voltage more than 8 V
- Ignition off.
- Control unit after-run completed
- Then ignition on

Possible fault causes
- DME main relay faulty (contact stuck)
- Short circuit to B+ in line between DME main relay and DME control unit (DME power supply)
- Short circuit to ground in line between DME main relay and DME control unit (DME relay activation)