Fuel Pump Relay

Fault symptom
The fuel pump relay does not work


Important: On 4-Cyl. cars the fuel pump relay is supplied with current via the +15 circuit and on 6-Cyl. cars it is supplied with current via the +30 circuit.







Diagnostic procedure
1 Check the fuel pump relay's power supply
- Unplug the fuel pump relay.
- Connect the test lamp to pin 86 of the relay socket and a good grounding point.
- The alarm should be disarmed.
- Ignition switch "ON" (+15).

The test lamp should light up.
Does it light up?
[YES] Continue fault diagnosis as described in "Powertrain Management/Computer and Control Systems", Trionic (4-Cyl. cars) or Motronic (6-Cyl. cars). Testing and Inspection
[NO] Continue with point 2.

2 Check the control module's power supply (+151+30 circuits)
- Remove the anti-theft alarm's control module.
- Connect the test lamp to pin 21 of the control module connector and a good grounding point.
- Ignition switch ON" (+15).

The test lamp should light up.
Does it light up?
[YES] Continue with point 4.
[NO] Continue with point 3.







3 Check the wiring
Check the continuity of the wiring between pin 21 of the control module's connector and:
- pin 87 of the main relay (6-Cyl.)
- fuse 13 (4-Cyl.)

The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 4.
[NO] Repair or replace the wiring harness.

4 Check the operation of the electronic control module
- Connect a jumper lead between pins 21 and 9 of the control module connector.
- Connect a test lamp to pin 86 of the connector and a good grounding point.
- Ignition switch "ON" (+15).

The test lamp should light up.
Does it light up?
[YES] Proceed to point 6.
[NO] Continue with point 5.







5 Check the wiring
Check the continuity of the wiring between pin 9 of the control module connector and pin 86 of the fuel pump relay.

The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Proceed to point 6.
[NO] Repair or replace the wiring harness.

6 Final test
- Start the car.
- Check to see if the fault symptom persists.

Does the trouble persist?
[YES] Continue as described in "Before Changing the Electronic Control Module". Before Changing the Electronic Control Module
[NO] The remedial measure taken was correct or the fault is of intermittent nature.