Chart A-5 Fuel Pump Relay Circuit Diagnosis

Chart A-5 Fuel Pump Relay Circuit:

Fuel Pump Relay Wiring Circuit:

Circuit Description:
When the ignition switch is turned "ON," the Engine Control Module (ECM) will activate the fuel pump relay and run the in-tank fuel pump. The fuel pump will operate as long as the engine is cranking or running and the ECM is receiving ignition reference pulses.

If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after key "ON."

Should the fuel pump relay or the 12 volts relay drive from the ECM fail, the fuel pump will continue to function by way of the oil pressure switch back-up circuit. Oil pressure will close the fuel pump side of the oil pressure switch, completing the circuit to the fuel pump.

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. The fuel pump relay is located in the passenger side engine compartment next to the shock tower.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. At this point, the fuel pump relay is operating correctly. The back-up circuit through the oil pressure switch is now tested.
2. After the fuel pump relay is replaced, continue with "Oil Pressure Switch Test."

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.

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. Refer to "Evaporative Emission (EVAP) Control System." Evaporative Emissions System

One or more leaking fuel injectors may also extend the cranking time. Perform the "Injector Balance Test" in CHART C2-A. Chart C-2A Injector Coil Test Procedure