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).
- 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 ..o 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 afterrun 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)