Fuel Pump Electrical Circuit Diagnosis
CIRCUIT DESCRIPTIONWhen the ignition switch is ON, the powertrain control module (PCM) activates the in-tank fuel pump. The fuel pump remains ON as long as the PCM receives the reference pulses from the ignition system. If there are no reference pulses, the PCM turns the fuel pump OFF after 2-3 seconds. The pump delivers fuel to the fuel rail and injectors. The fuel pressure regulator, located in the fuel tank, maintains the system pressure at 380-410 kPa (55-60 psi). 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.
Incorrect 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 set
TEST DESCRIPTION
Steps 1-6:
Steps 7-17:
Steps 18-29:
The numbers below refer to the step numbers on the diagnostic table.
2. Command both the ON and OFF states. Repeat the commands as necessary.
3. This step determines whether the condition is located on the coil side or on the switch side of the circuit.
4. This step verifies that the powertrain control module is providing voltage to the fuel pump relay.
5. This step tests for an open in the ground circuit to the fuel pump relay.
6. This step determines if a voltage is constantly being applied to the fuel pump relay.
12. This step determines if the condition is between the fuel pump relay and the body pass through connector.
15. This step tests if the relay is causing the condition. Use a fused jumper wire with a 20-ampere fuse.
16. This step determines if the condition is between the fuel pump relay and the body pass-through connector.
17. This step verifies if the fuel pump ground circuit is causing the condition. Inspect all connections for corrosion or for poor connections.
18. A condition with the fuel pump jumper harness can cause the pump to be inoperative. Carefully inspect the fuel pump jumper harness.
20. This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.