Fuel Pump Electrical Circuit Diagnosis
FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSISCIRCUIT DESCRIPTION
The circuit opening relay provides ignition positive voltage to the fuel pump. The circuit opening relay is controlled by the powertrain control module (PCM) and receives ignition positive voltage from the EFI relay. The PCM monitors the crank signal circuit for voltage when the ignition switch is in the START (engine cranking) position. When the crank signal circuit indicates the engine is cranking the PCM energizes the circuit opening relay. The PCM also energizes the circuit opening relay whenever starter switch indicates cranking. If the CKP signal circuit does NOT indicate cranking, the PCM energizes the circuit opening relay based on starter switch input.
DIAGNOSTIC AIDS
Check for any of the following conditions:
- The resistance of the circuit opening relay-The resistance across terminal 3 and terminal 4 is 85-95 ohms at 20°C (68°F). The resistance across terminal 1 and terminal 2 is infinite.
- The circuit opening relays electrical contacts may be pitted or sticking. Replace the relay if tapping gently on the relay or wiggling the relay causes a change in the relays operation.
- The performance of the circuit opening relay may be affected by temperature. Check the 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 following 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
Steps 1-5:
Steps 6-9:
Steps 10-15:
Steps 16-22:
The numbers below refer to the step numbers on the diagnostic table.
1. The Diagnostic System Check-Computers and Controls Systems prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks for the operation of the fuel pump. Fuel pump operation is difficult to hear without seat cushion removal.
5. This step checks for the operation of the circuit opening relay. The circuit opening relay is located just above the left side kick panel and makes an audible click when turning ON and OFF.
7. This step checks the control circuit of the fuel pump relay.
9. The most likely location of an open circuit is between the splice and circuit opening relay terminal 2. An inoperative EFI relay would cause no MIL operation. The EFI relay is diagnosed in the No Malfunction Indicator Lamp diagnostic table.
10. This step checks for a fault in the fuel pump or the circuit from the circuit opening relay to the fuel tank. The vehicle should start and run if the only fault was with the circuit opening relay.