Chart A-5, Fuel Pump Relay Circuit: Notes

When the ignition switch is turned to the "ON" position, the ECM will turn on the electric fuel pump by energizing the fuel pump relay. The ECM will keep the pump on if the engine is running or cranking (ECM is receiving reference pulses from the ignition module). If there are no reference pulses, the ECM turns pump off within 2 seconds after key on. Normal pump pressure is approximately 35-38 psi (2.5-2.7 kg/cm² ) with the vacuum hose disconnected from the pressure regulator. Excess fuel is returned to the tank. When the engine is stopped, the pump can be turned on by applying battery voltage to the fuel pump test terminal, located in the engine compartment.

1. This test confirms the ECM is operating the fuel pump. Since the engine is not running and the ECM is not receiving reference pulses, the fuel pump relay will be turned off after 2 seconds.
2. This test turns pump on if circuit No. 120 is okay.
3. Checks relay ground circuit No. 450.
4. If fuse is blown, this test will confirm a short to ground in circuit No. 120. To prevent mis-diagnosis, be sure fuel pump is disconnected before test.
5. Checks for battery voltage at pump relay.
6. This test checks for ECM control of relay through circuit No. 465.
7. The fuel pump control circuit includes an oil pressure switch, parallel to the relay. Should the relay fail, the switch will provide voltage to the pump as long as oil pressure is more than 4 psi. If the relay fails, engine crank time may be extended because pump relay will not activate fuel pump until engine builds up oil pressure. If engine cranks slowly or switch is defective, engine may not start.
8. This test checks if oil pressure switch provides voltage to pump.
9. This test checks that oil pressure switch is open when engine is not running. Switch sticking closed will allow pump to run continuously and discharge battery.