Fuel Pump Relay: Testing and Inspection

Fuel Primer Relay J643, Checking

Special tools, testers and auxiliary items required
- Multimeter.
- wiring diagrams.

Test requirements
- Fuse SB42 OK.
- The Ground (GND) connections at the engine and transmission OK.
- The battery voltage at least 12.5 V.
- The generator OK.

Test procedure
- Perform a preliminary check to verify the customers complaint.

Start diagnosis
- Using a Multimeter, check the following wiring connection for voltage.

Fuel Primer Relay J643 socket Measure to
21/31 Engine Ground (GND)

Specified value: 12.5 V

If the specified value was not obtained:
- Check the Fuel Primer Relay J643 socket 1/30 to the Battery for an open circuit or short to Ground (GND).
- Check the electrical harness connectors for damage, corrosion, loose or broken terminals.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:
- Using a Multimeter, check the following wiring connection for voltage.

Fuel Primer Relay J643 Measure to
23/87 Engine Ground (GND)

- Crank the engine.

Specified value: 12.5 V

- Switch the ignition off.

If the specified value was not obtained:
- Check the Fuel Primer Relay J643 socket 3/86 to the Power Supply Relay (terminal 15) J329 socket 2/87 for an open circuit or short to Ground (GND).
- Check the electrical harness connectors for damage, corrosion, loose or broken terminals.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:

Checking Ground (GND)

If the manufacturers test box is being used. Perform the following step.
- Install the test box.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) J220.
- Using a Multimeter, check the following wiring connection for resistance.

Fuel Primer Relay J643 socket Motronic Engine Control Module
(ECM) J220 electrical harness
connector T121 or test box socket
16/MOT 65

Specified value: 1.5 ohms

If the specified value was not obtained:
- Check the Fuel Primer Relay J643 socket 16/MOT to the Motronic Engine Control Module (ECM) J220 electrical harness connector T121 terminal 65 for an open circuit or a short to Battery (+).
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring and the voltage supply was OK:
- Replace the Fuel Primer Relay J643.
- Perform a road test to verify repair.

If the fault does not return:

Repair complete, Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
- End diagnosis.

If the fault does return and no malfunction is detected in the wiring and the voltage supply was OK:
- Replace the Motronic Engine Control Module (ECM) J220.
- Assembly is performed in the reverse of the removal.

Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Reading Diagnostic Trouble Codes
2. If necessary, erase the DTC memory. Clearing Diagnostic Trouble Codes
3. If the DTC memory was erased, generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

End diagnosis.