Circuit Diagnosis - Fuel Pump Relay

Diagnostic Chart:

Wiring Diagram:

Circuit Description

When the ignition switch is turned ON, the Vehicle Control Module (VCM) turns the in-tank fuel pump ON. The in-tank fuel pump remains ON as long as the engine is cranking or running and the VCM is receiving the distributor reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after the ignition is ON or the engine stops.

Should the fuel pump relay or the 12 volt relay drive from the VCM fail, the fuel pump receives a supply current through the oil pressure switch backup circuit. The fuel pump test terminal is located in the drivers side of the engine compartment. When the engine is stopped, applying the battery voltage to the test terminal can turn on the fuel pump.

Diagnostic Aids

An inoperative fuel pump relay can result in long cranking times. The time necessary for the oil pressure to reach the pressure required in order to close the oil pressure switch and supply the necessary current for the fuel pump causes the extended crank period. If the fuel pump relay circuit checks out OK, refer to Fuel System Diagnosis (System Check). System Check

Excessive fuel may also cause long cranking times which is accompanied by the following conditions:

1. A start that is not as fast as normal

2. A puff of black smoke at the tailpipe

An improperly connected or faulty EVAP canister control valve can cause this problem. Disconnect the [1][2]EVAP purge hose from the EVAP canister control valve in order to diagnose. Refer to EVAP Control System Diagnosis. System Diagnosis - EVAP Control

One or more leaking poppet nozzles may also extend the cranking time. Perform the Poppet Nozzle Test, in the Injector Balance Test Table. Refer to Fuel Injector Balance Test. Fuel Injector Balance Test

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. This step checks for the correct operation of the fuel pump.

3. This step checks the operation of the fuel pump by supplying 12 volts to the fuel pump control circuit.

5. This step checks the battery feed circuit to the fuel pump relay.

10. This step checks for the proper operation of the fuel pump relay.