Fuel Pump Relay

Fault symptom
The fuel pump relay does not work







Diagnostic procedure
1 Check the engine management system's power supply
- Unplug connector H33-1.
- Connect the test lamp to pin 30 of connector H33-1 and a good grounding point.
- Turn the ignition switch to the "ST" position (+50).
The test lamp should flash during starter motor cranking.
Does it flash?
[YES] Continue with point 2.
[NO] Proceed to point 4.

2 Check the wiring between connectors H33-1 and H33-4
Check the wiring harness for continuity between pin 30 of connector H33-1 and pin 11 of connector H33-4.
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 3.
[NO] Repair or replace the wiring harness.







3 Check the wiring connected to the engine management system
Check the wiring harness for continuity between pin 11 of connector H33-4 and Pin 56 of the Trionic electronic control module.
- Pin 3 of the Motronic 2.10.3 electronic control module.
- Pin 3 of the Motronic 2.8.1 electronic control module depending on the engine version.
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue fault diagnosis as described in "Powertrain Management".
[NO] Repair or replace the wiring harness







4 Check the operation of the fuel pump relay Plug in connectors H33-1 and H33-4.
- Unplug the fuel pump relay.
- Connect the test lamp to pins 86 and 85 of the fuel pump relay socket.
- Turn the ignition switch to the ST position (+50).
The test lamp should flash during starter motor cranking.
Does it flash?
[YES] Continue fault diagnosis as described in "Engine management system "TRIONIC" or "MOTRONIC".
[NO] Continue with points.







5 Check the operation of the fuel pump relay
- Connect the test lamp to pins 85 and 30 of the fuel pump relay socket.
- Turn the ignition switch to the "ST" position (+50).
The test lamp should flash during starter motor cranking.
Does it flash?
[YES] Continue fault diagnosis as described in "Powertrain Management".
[NO] Continue with point 6.

6 Check the wiring
Check the wiring harness for continuity between pin 85 of the fuel pump relay socket and pin 29 of connector H33-3.
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 7.
[NO] Repair or replace the wiring harness.







7 Check the wiring connected to the electronic control module
- Unplug the control module.
- Check the wiring harness for continuity between.
- connector H33-1 (pin 30) and the electronic control module (pin 21).
- connector H33-3 (pin 29) and the electronic control module (pin 9).
The resistance should be < 1 ohm.
Is the resistance OK?
[YES] Continue with point 8.
[NO] Repair or replace the wiring harness.

8 Final test
Start the car and check to see if the fault symptom persists.
Does the trouble persist?
[YES] Continue as described in "Before Changing The Electronic Control Module".
[NO] The remedial measures taken were correct or the fault is of intermittent nature.