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Auxiliary Fuel Pump Checking

Special tools and workshop equipment required 

Test conditions 

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK 

Start diagnosis 

-- Disconnect the electrical harness connector from the Auxiliary Fuel Pump -V393- (left side of engine compartment).

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

Specified value: 1.0 Ohm (+/-.5 ohm).

-- 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 30 of the Fuel Pump Relay -J49-.

The test lamp should be ON.

-- Using a test lamp connected to ground, touch terminal 86 of the Fuel Pump Relay -J49-.

The test lamp should be ON.

-- Turn the ignition OFF.

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

-- Check the circuit between the Fuel Pump Relay -J49- terminal 30 to fuse S - 11, or Fuel Pump Relay -J49- terminal 86 to fuse S - 7 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- T94/72 terminal.

Specified value: 1.5 Ohm 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 87 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 terminal T94/4 of the Motronic Engine Control Module (ECM) -J623- 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 .
  2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
  3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .
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