Fuel Pump Relay/Fuel Pump Test

Fault Symptom.
Engine fails to start.

Diagnostic Help.
The output stage for activation of the fuel pump relay is monitored by the Motronic system. See diagnostic trouble codes P1501, P1502, P1541.

Check The Wiring.
Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.





Diagnostic Procedure.
1. Check the fuses
- Check fuse 14 (fuel pump power supply via fuel pump relay)

Is the fuse intact?

YES: Continue with point 2.
NO: Change the fuse and start the engine. Check whether the fuse blows. If it does, continue with point 6.

2. Check the performance of the fuel pump
- Forcibly actuate the fuel pump by connecting a jumper lead between fuses 14 and 22.
The fuel pump should start working.

Is the pump working?

YES: Continue with point 3.
NO: Continue with point 5.





3. Check the current applied to the pump relay
- Unplug the pump relay.
- Connect a test lamp to pin 30 of the relay socket and a good ground.
The test lamp should light up.

Test lamp on?

YES: Continue with point 4.
NO: Check and if necessary repair or replace the lead between pin 30 of the relay socket and crimped connection J73.





4. Check the fuel pump relay
- Connect a jumper lead between pins 30 and 87 of the relay socket.
- Listen for the sound of the fuel pump working.

Is the fuel pump working?

YES: Change the fuel pump relay.
NO Check and if necessary repair or replace the lead between pin 87 of the relay socket and fuse 14.





5. Check the fuel pump
- Unplug connector H4-4 from the fuel pump. The connector is located adjacent to the fuel pump under the luggage compartment floor.
- Connect a test lamp to pins 1 and 2 of the 2-pin connector.
- Connect the ISAT Scan Tool.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "PUMP RELAY".

The test lamp should flash at a frequency of 1 Hz (once per second).

Test lamp flashing?

YES: Check and if necessary change the fuel pump.
NO: First check and if necessary repair or replace the lead between pin 2 and grounding point G5. If this does not help, deal with the lead between pin 1 and fuse 14 in the same way.





6. Check the fuel pump
- Unplug connector H4-4 from the fuel pump. The connector is located adjacent to the fuel pump under the luggage compartment floor.
- Change fuse 14.
- Connect the ISAT Scan Tool.
- Turn the ignition switch to the ON position.
- Select "ACTIVATE".
- Select "PUMP RELAY".

Did the fuse blow?

YES: Check and if necessary repair or replace the wiring harness between fuse 14 and pin 1 of connector H4-4.
No: Change the fuel pump.