Fuel pump relay
Symptom: Fuel pump relay not working
Fault symptom
Fuel pump relay not working
Diagnostic procedure
1 Check the engine management system's power supply
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Unplug connector H33-1.
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Connect the test lamp to pin 30 of connector H33-1 and a good grounding point.
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Turn the ignition switch to the "ST" position (+50).
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The test lamp should flash during starter motor cranking.
Is the test lamp flashing?
Continue with point 2.
Continue with 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 correct?
Continue with point 3.
Repair or replace the wiring harness.
3 Check the wiring connected to the engine management system
Conduct a continuity test on the cable assembly between connector H33-4, pin 11 and
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Trionic control module, pin 56.
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Motronic 2.10.3 control module, pin 3
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Motronic 2.8.1 control module, pin 3
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depending on the engine alternative. The resistance should be < 1 Ohm.
Is the resistance correct?
Continue fault diagnosis as described in Service Manual 2:7 "Engine management system TRIONIC", "MOTRONIC 2.10.3" or "MOTRONIC 2.8.1".
Repair or replace the wiring harness.
4 Check the operation of the fuel pump relay
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Plug in connectors H33-1 and H33-4.
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Unplug the fuel pump relay.
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Connect the test lamp to pins 86 and 85 of the fuel pump relay socket.
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Turn the ignition switch to the "ST" position (+50).
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The test lamp should flash during starter motor cranking.
Is the test lamp flashing?
Continue fault diagnosis as described in Service Manual 2:7 "Engine management system "TRIONIC", "MOTRONIC 2.10.3" or "MOTRONIC 2.8.1".
Continue with point 5.
5 Check the operation of the fuel pump relay (contd.)
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Connect the test lamp to pins 85 and 30 of the fuel pump relay socket.
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Turn the ignition switch to the "ST" position (+50).
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The test lamp should flash during starter motor cranking.
Is the test lamp flashing?
Continue fault diagnosis as described in Service Manual 2:7 "Engine management system "TRIONIC", "MOTRONIC 2.10.3" or "MOTRONIC 2.8.1".
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 correct?
Continue with point 7.
Repair or replace the wiring harness.
7 Check the wiring connected to the electronic control module
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Unplug the control module.
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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).
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The resistance should be < 1 ohm.
Is the resistance correct?
Continue with point 8.
Repair or replace the wiring harness.
8 Final check
Start the car and check to see if the fault symptom remains.
Is the problem still present?
See "Before replacing a control module".
The remedial measures taken were correct or the fault is of intermittent nature.
