Fuel Pump Electrical Circuit Diagnosis
CIRCUIT DESCRIPTIONWhen you turn ON the ignition switch, the control module enables the fuel pump relay which powers the fuel pump ON. The fuel pump remains ON as long as the engine is cranking or running and the control module receives ignition reference pulses. If there are no ignition reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position or if the engine stops.
The electric fuel pump is attached to the fuel sender assembly inside the left fuel tank. The in-tank fuel pump supplies fuel through a fuel feed pipe, a fuel filter/fuel pressure regulator assembly, to the fuel rail. The fuel pump supplies fuel to the siphon jet pump of the right fuel tank. This allows the pump to transfer fuel from the right fuel tank to the left fuel tank. The fuel pump provides fuel at a pressure that is above the pressure needed by the fuel injectors. The fuel pressure regulator, part of the fuel filter, keeps the fuel available to the fuel injectors at a regulated pressure. Unused fuel returns to the left fuel tank by a separate fuel return pipe.
DIAGNOSTIC AIDS
The following conditions may have caused the fuel pump fuse to open:
^ The fuse was faulty.
^ There is an intermittent short in the power feed circuit of the fuel pump.
^ The fuel pump has an internal intermittent condition.
For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions
TEST DESCRIPTION
Steps 1-14:
Steps 15-27:
The numbers below refer to the step numbers on the diagnostic table.
2. Command the ON and the OFF states. Repeat the commands as necessary.
3. This step determines if 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 tests for a grounded supply circuit between the fuel pump relay and the harness connector of the fuel pump.
13. 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.
15. This step determines if the fuel pump relay is causing the condition. Use the appropriate-size fused jumper wire.
16. This step tests for an open, or for excess resistance in the supply circuit between the relay and the harness connector of the fuel pump.
17. Inspect the fuel pump ground circuit thoroughly. Corrosion or a poor connection may cause the fuel pump stop operating.
18. This step inspects for a poor connection or for corrosion at the fuel pump harness connector which may cause the condition.