Fuel Pump Electrical Circuit Diagnosis
CIRCUIT DESCRIPTIONThe powertrain control module (PCM) energizes the fuel pump relay for 3 seconds when the ignition switch is turned to the ON position. When the fuel pump relay is energized the fuel pump will operate and pressurize the fuel system. When the engine is being cranked, or is running, the PCM will receive ignition system reference pulses and will continue to energize the fuel pump relay as long as ignition system reference pulses are detected. The fuel pump will stop after 3 seconds when the ignition is On, unless the PCM receives ignition system reference pulses.
DIAGNOSTIC AIDS
Check for any of the following conditions:
- Check the resistance of the fuel pump relay. The resistance across terminal 3 and terminal 5 is 79-95 ohms at 20°C (68°F). The resistance across terminal 1 and terminal 2 is infinite.
- The fuel pump relay electrical contacts may be pitted or sticking. Replace the fuel pump relay if tapping gently on the relay or wiggling the relay causes a change in the relay operation.
- The performance of the fuel pump relay may be affected by temperature. Check the fuel pump relay after sitting outside overnight and after running the engine 30 minutes.
An intermittent malfunction may be caused by a fault in the fuel pump electrical circuit. Refer to Intermittent Conditions. Intermittent Conditions
Use the relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.
TEST DESCRIPTION
Step 1:
Steps 2-6:
Steps 7-9:
Steps 10-13:
Steps 14-19:
Steps 20-24:
The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems prompts the technician to complete some basic checks, and to save the applicable Freeze Frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The electronic copy can then be referred to for later reference.
2. This step determines if the fuel pump relay can operate the fuel pump.
5. This step checks the control circuit of the fuel pump relay.
7. This step determines if the coil side of the fuel pump circuit is operating correctly.
10. This step checks for an electrical fault in the fuel tank or in the fuel pump wire harness.
17. This step determines whether the switched side of the fuel pump relay is always closed.