Fuel Pump Electrical Circuit Diagnosis

FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS

Schematic:

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

CIRCUIT DESCRIPTION
When 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 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
^ Diagnostic Trouble Codes (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.

2. Command both the ON and OFF states. Repeat the commands as necessary.

3. This step determines if the condition is located on the coil side or the switch side of the circuit.

4. This step verifies that the PCM 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. To gain access to the fuel pump connector, the fuel tank may need to be removed.

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. Use the same amperage fuse in the jumper as is used to protect the fuel pump circuit.

16. To gain access to the fuel pump connector, the fuel tank may need to be removed.

17. Inspect the ground connection for the fuel pump. Be certain all ground connections are clean and tight.