P0685

P0685

Diagnosis information - Control unit DME (DFI)

Start delay due to undervoltage

Diagnostic conditions
- Control unit DME (DFI) is viable (voltage > 5 V at A34 (terminal 15) + ground)
- Ignition is switched on (voltage present at A34)

Possible fault causes
- If the actual value [A010DME SUPPLY VOLTAGE] in the Freeze-frame of the fault entry P0685 was stored at < 8.0 V:
- Voltage is too low or voltage drops when the engine starts (See [Information]).

- If the actual value [A010DME SUPPLY VOLTAGE] in the Freeze-frame of the fault entry P0685 was stored at > 8.0 V:
- Open circuit Power supply Control circuit Main relay
- Short circuit to ground or open circuit in lines between Main relay and Control unit DME (DFI) (Power supply Control unit DME (DFI))
- Short circuit to B+ or open circuit in lines between Control unit DME (DFI) and Main relay (Activation Main relay relay)
- Main relay Faulty

Fault setting condition(s)
- A check is carried out once to determine whether the voltage at A3/A5/A6 has exceeded a minimum value :
- Panamera > 6.0 V
- Cayenne with program version up to WS5880 > 6.0 V
- Cayenne with program version WS5890 or higher (week 45/10) > 5.0 V

- Test duration 0.0 to approx. 0.5 seconds after ignition on, or after control unit reset.

Fault effects
- Fuel injection is blocked.

INFORMATION
- According to specifications, the DME main relay must function only at 8.0 V or higher.
- There are also relays that work at a significantly lower voltage.
- The entire engine control system can work at 5.0 V or higher.
- If the start voltage drops, this can cause the diagnosis to detect the fault [START DELAY DUE TO UNDERVOLTAGE] and fuel injection will be blocked.
- The starter relay can also pick up at 3 V.
- This means that the starter might still turn, but the engine cannot start.
- The various software versions can result in various types of behavior and displays:

I. Possible behavior and displays in the Panamera and Cayenne with program version up to WS5880:
- Start voltage < 5 V:
- Starter might turn
- Engine does not start
- NO DME fault entries because the DME (DFI) control unit is not viable.

- Start voltage Less than 5 V, but Greater than 5 V ... < 6 V before and after the start attempt + DME main relay does NOT function:
- Starter might turn
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.
- DME fault entry P1572 because the control unit voltage dropped to < 5 V and as a result, control unit run-on could not be completed.

- Start voltage Less than 5 V, but Greater than 5 V ... < 6 V before and after the start attempt + DME main relay is working:
- Starter might turn
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] > 5 V ... < 6 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.
- DME fault entry P1572 because the control unit voltage dropped to < 5 V and as a result, control unit run-on could not be completed.

- Start voltage > 5 V ... < 6 V + DME main relay does NOT function:
- Starter might turn
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.

- Start voltage > 5 V ... < 6 V + DME main relay is working:
- Starter turns
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] > 5 V ... < 6 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.

- Start voltage > 6 V ... < 8 V + DME main relay does NOT function:
- Starter turns
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.

- Start voltage > 6 V + DME main relay is working:
- Starter turns
- Engine starts
- NO DME fault entries

- Start voltage > 8 V + DME main relay does NOT function:
- Starter turns
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- DME fault entry P0686 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V

II. Behavior and displays in the E2 with WS5890 or higher:
- Start voltage < 5 V:
- Starter might turn
- Engine does not start
- NO DME fault entries because the DME (DFI) control unit is not viable.

- Start voltage > 5 V ... < 8 V + DME main relay does NOT function:
- Starter turns
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- NO DME fault entry P0686 because these diagnostic conditions (> 8.0 V at A34) were not met.

- Start voltage > 5 V ... < 8 V + DME main relay is working:
- Starter turns
- Engine starts
- NO DME fault entries

- Start voltage > 8 V + DME main relay does NOT function:
- Starter turns
- Engine does not start
- DME fault entry P0685 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V
- DME fault entry P0686 with Freeze-frame actual value [A010DME SUPPLY VOLTAGE] = 0 V

- Start voltage > 8 V + DME main relay is working:
- Starter turns
- Engine starts
- NO DME fault entries