Circuit Diagnosis - Fuel Pump Relay

Diagnostic Chart:

Wiring Diagram:

Circuit Description

When the ignition switch is first turned on, the PCM energizes the fuel pump relay which applies power to the in-tank fuel pump. The fuel pump relay will remain on as long as the engine is running or cranking and the PCM is receiving reference pulses. If no reference pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned or the engine is stopped.

The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator, a vacuum sensitive device, controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the engine stopped, the fuel pump can be turned on by using a fused jumper to apply battery positive voltage to the fuel pump test lead in the engine compartment.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following items:

- Poor connection or damaged harness.

- Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Test Description

The number(s) below refer to the Step number(s) on the Diagnostic Table:

2. Verifies that the fuel pump feed circuit is OK between the fuel pump relay and the fuel pump, and that the fuel pump can deliver adequate pressure to the fuel rail.

3. Checks the fuel pump relay battery positive voltage feed and relay coil ground circuits.

4. Ensures that the fuel pump relay driver circuit and the PCM are capable of controlling the fuel pump relay.

5. Checks the fuel pump driver circuit for a short to ground.

6. Checks the fuel pump driver circuit for an open.

10. If the fuel pump is operating but incorrect pressure is noted, the fuel pump wiring is OK. The Fuel System Diagnosis should be used for diagnosis.

11. Checks the fuel pump feed circuit between the fuel pump relay and the fuel pump. Also checks the fuel pump ground circuit.

12. Determines whether the problem is being caused by an open in the fuel pump feed circuit or the fuel pump ground circuit.