Auxiliary Fuel Pump Checking

Auxiliary Fuel Pump Checking

Special tools, testers and auxiliary items required

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• Multimeter.

• Electrical connector test lead set.

Test conditions

• Battery voltage 12.5 V.

• Fuse 27 in Fuse Panel C is OK.

• Fuel filter OK.

• Ignition switched off.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

- Disconnect the electrical harness connector from the Auxiliary Fuel Pump (V393) (right side of engine. See repair information, auxiliary fuel pump removal for location).

- Connect a multimeter to both terminals of the Auxiliary Fuel Pump (V393) connector and check the motor resistance.

Specified value: 1.4ohms (+/-.5 ohms).

- If the Specified value was Not obtained, replace the Auxiliary Fuel Pump (V393)

- If the Specified value was obtained:

- Remove the Fuel Pump Relay (J49).

- Turn the ignition ON.

- Using a test lamp connected to ground, touch terminal 1 of the Fuel Pump Relay (J17).

The test lamp should be ON.

- Using a test lamp connected to ground, touch terminal 3 of the Fuel Pump Relay (J17).

The test lamp should be ON.

If the test lamp was Not ON for any above test:

- Check the circuit between the Fuel Pump Relay (J17) terminal 3 to fuse 15 in Fuse panel B for an open, short to ground or high resistance.

If the test lamp was ON for both tests:

- Turn the ignition OFF.

- Install a jumper from relay terminal 30 to relay terminal 87.

- Turn the ignition ON.

The Auxiliary Fuel Pump (V393) should operate.

- If the Auxiliary Fuel Pump (V393) does operate:

- Replace the Fuel Pump Relay (J49) and retest for operation.

- If the Auxiliary Fuel Pump (V393) still does Not operate:

- Remove the Motronic Engine Control Module (ECM) (J623). Refer to the repair information for removal instructions.

- Check the resistance of the circuit from relay terminal 85 to the Motronic Engine Control Module (ECM) (J623) T60/15 terminal.

Specified value: 1.5 ohms or less.

- If the specified value was not obtained, repair the circuit between the relay and the ECM for an open, high resistance or short.

- If the specified value was obtained, replace the Motronic Engine Control Module (ECM) (J623). Refer to the repair information for removal instructions.

- If the Auxiliary Fuel Pump (V393) did Not operate with the jumper connected:

- Leave ignition ON and jumper connected.

- Connect a test lamp to ground and touch terminal 2 of the Auxiliary Fuel Pump (V393) electrical harness connector.

The test lamp should be ON.

- If the test lamp is Not ON, check for an open circuit between the relay terminal 42 and the Auxiliary Fuel Pump (V393) harness connector terminal 2 for an open or high resistance. Repair as necessary.

- If the test lamp is ON, remove the test lamp from engine ground and connect it to terminal 1 of the Auxiliary Fuel Pump (V393) connector. Touch the other end of the test lamp to terminal 2.

- The test lamp should be ON.

- If the test lamp is Not ON, check for an open circuit between the Auxiliary Fuel Pump (V393) harness connector terminal 1 to ground for an open or high resistance. Repair as necessary.

- If the test lamp was ON, replace the Auxiliary Fuel Pump (V393).

Final procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 0A.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 0A.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.