Fuel Pump Relay Circuit Diagnosis

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 on 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 controls fuel pressure by allowing excess fuel to be returned to the fuel tank.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for a poor connection or damaged harness. Inspect the PCM harness and connectors for the following items:
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal to wire connections
^ Damaged harnesses

Test Description

The numbers below refer to the step numbers on the Diagnostic Table:
2. Tests the ignition feed circuit to the fuel pump relay.
3. 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.
4. Tests the fuel pump feed circuit for a short to battery positive voltage.
8. Tests whether the problem is being caused by an open in the fuel pump feed circuit or the fuel pump ground circuit.