Fuel Pump Relay Circuit Diagnosis

FUEL PUMP RELAY CIRCUIT DIAGNOSIS















Circuit Description
When the ignition switch is ON, the PCM activates the in-tank fuel pump. The fuel pump remains ON as long as the PCM receives reference pulses from the ignition system. If there are no reference pulses, the PCM turns the fuel pump OFF after about 2-3 seconds. The pump delivers fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure remains at 379-427 kPa (55-62 psi) while the fuel pump is running. Excess fuel returns to the fuel tank. When the engine is stopped, a scan tool in the output controls function can turn ON the fuel pump.

Improper fuel system pressure results in one or many of the following symptoms:
^ Cranks but will not run
^ Cuts out, may feel like an ignition problem
^ Poor fuel economy
^ Loss of power
^ Hesitation
^ DTCs

Diagnostic Aids
A fuel pump prime terminal is available at the Underhood Bussed Electrical Center (UBEC). Refer to the UBEC cover for terminal location.
The following conditions may have caused the fuel pump fuse to open:
^ The fuse is faulty
^ There is an intermittent short in the fuel pump power feed circuit.
^ The fuel pump has an intermittent internal problem.

For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. Refer to the wiring schematic for the proper terminal identification.
5. The test lamp only illuminates for two seconds even though the scan tool commanded position is ON. You will have to command the fuel pump OFF then ON to re-enable the PCM fuel pump control.
7. The fuel pump harness connector can be accessed between the frame rail and the fuel tank.
12. Inspect the fuel pump fuse for an open. If the fuse is open, inspect the circuit for a short to ground.
20. Inspect the fuel pump fuse for an open. If the fuse is open, inspect the circuit for a short to ground.