Chart A-5 Fuel Pump Relay Circuit Diagnosis

Chart A-5:

Fuel Pump Relay Circuit:

Circuit Description
When the ignition switch is turned "ON," the control module will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving ignition reference pulses. If there are no reference pulses, the PCM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.

Should the fuel pump relay or the 12 volt relay drive from the PCM fail, the fuel pump will receive supply current through the oil pressure switch back-up circuit.

The fuel pump "test" terminal is located in the driver's side of the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the "test" terminal.

Chart Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following step will locate.

2. This step checks voltage from the battery and the ground circuit to the relay.

3. This test determines if there is voltage from the PCM terminal, "F6" to the relay connector.

4. This step completes the fuel pump relay circuit but if this diagnosis was used because the engine would not run then the oil pressure switch should also be diagnosed.

Diagnostic Aids
An inoperative fuel pump relay can result in long cranking times. The extended crank period is caused by the time necessary for oil pressure to reach the pressure required to close the oil pressure switch and supply the necessary current for the fuel pump.

If the fuel pump relay circuit checks out OK, refer to "Fuel System Diagnosis," CHART A-6. Related Tests, Information and Procedures

Excess fuel may also cause long cranking times. This would usually be accompanied by a start that is not as fast as normal (once fired, the engine does not build up speed as fast) and a puff of black smoke at the tailpipe. An improperly connected or faulty EVAP canister control valve can cause this problem. Disconnect the "EVAP purge hose" from the "EVAP canister control valve" to diagnose.

One or more leaking fuel injectors may also extend the cranking time. Perform the "Injector Balance Test," CHART A-7. Chart A-7 Injector Balance Test