Fuel System Electrical Test
Circuit Description
When the ignition switch is first turned "ON", the powertrain control module (PCM) energizes the fuel pump relay which applies power to the in tank fuel pump. The fuel pump relay will remain "ON" as long as the Engine is running or cranking and the PCM is receiving 58X Crankshaft position pulses. If no 58X Crankshaft position pulses are present, the PCM de-energizes the fuel pump relay within 2 seconds after the ignition is turned "ON" or the Engine is stopped.
The fuel pump delivers fuel to the fuel rail and injectors, then to the fuel pressure regulator. The fuel pressure regulator controls fuel pressure by allowing excess fuel to be returned to the fuel tank. With the Engine stopped and ignition "ON", the fuel pump can be turned "ON" by using a command by the Scan Tool.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside the insulation. Check for the following items:
- Poor connection or damaged harness - Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness.
Test Description
Number(s) below refer to the step number(s) in the Diagnostic Test:
2. If the fuel pump is operating but incorrect pressure is noted, the fuel pump wiring is OK and the "Fuel System Pressure Test" chart should be used for diagnosis.
WARNING: To reduce the risk of fire and personal injury:
- It is necessary to relieve fuel system pressure before connecting a fuel pressure gauge.
- A small amount of fuel may be released when disconnecting the fuel lines. Cover fuel line fittings with a shop towel before disconnecting, to catch any fuel that may leak out. Place the towel in an approved container when the disconnect is completed.
Fuel Pressure Relief Procedure
1. Remove the Fuel Cap.
2. Remove the fuel pump relay from the underhood relay center.
3. Start the Engine and allow it to stall.
4. Crank the Engine for an additional 3 seconds.
Fuel Gauge Installation
1. Remove the shoulder fitting cap.
2. Install fuel gauge J 34730-1 to the fuel feed line located in front of and above the right side valve cover.
3. Reinstall the fuel pump relay.
Diagnostic Test
1. Was the On-Board Diagnostic (OBD) System Check" performed?
[YES] Go to Step 2.
[NO] Go to OBD System Check. Initial Inspection
2. a. Read the "Caution" in Test Description.
b. Relieve the fuel system pressure and install the fuel pump pressure gauge to the test fitting.
c. Use a Scan Tool to command the fuel pump "ON."
d. Is there an immediate pressure build-up which indicates the pump is running?
[YES] Go to Step 3.
[NO] Go to Step 4.
3. a. Verify that the pump is not running by removing the fuel filler cap and listening.
b. Command the pump "ON" with the Scan Tool.
c. Did the pump turn "OFF" after 2 seconds?
[YES] Test completed.
[NO] Go to Step 12.
4. a. Ignition "OFF".
b. Remove the fuel pump relay.
c. Using a test light connected to ground, probe the battery feed to the relay.
d. Did the light illuminate?
[YES] Go to Step 6.
[NO] Go to Step 5.
5. a. Repair short or open battery feed to fuel pump relay.
b. Is the action complete?
[YES] Verify repair.
6. a. Connect a test light between the two wires that connect to the fuel pump relay pull-in coil.
b. Ignition "ON".
c. Did the test light illuminate for 2 seconds and then turn off?
[YES] Go to Step 12.
[NO] Go to Step 7.
7. a. With a test light connected to battery (-), probe the fuel pump relay connector at the wire which runs from the relay pull-in coil to the PCM.
b. Ignition "ON".
c. Did the test light illuminate for 2 seconds and then turn off?
[YES] Go to Step 8.
[NO] Go to Step 9.
8. a. Locate and repair open in the fuel pump relay ground circuit.
b. Is the action complete?
[YES] Verify repair.
9. a. Check for short or open between the PCM and the fuel pump relay.
b. Was a problem found?
[YES] Verify repair.
[NO] Go to Step 10.
10. a. Check the fuel pump relay circuit for a poor terminal connection at the PCM.
b. If a problem is found, replace terminal as necessary.
c. Was a problem found?
[YES] Verify repair.
[NO] Go to Step 11.
11. a. Replace the PCM.
IMPORTANT: The replacement PCM must be programmed.
b. Is the action complete?
[YES] Verify repair.
12. a. Reconnect the fuel pump relay.
b. Disconnect the fuel pump electrical connector at the fuel tank.
c. Using a test light connected to ground, probe the fuel pump feed wire (harness side).
d. Command the fuel pump "ON" with a Scan Tool.
e. Did the light illuminate for 2 seconds?
[YES] Go to Step 15.
[NO] Go to Step 13.
13. a. Honk the horn to verify that the horn relay is functioning.
b. Substitute the horn relay for the fuel pump relay.
c. Leave the test light connected as in step 12.
d. Command the fuel pump "ON" with the Scan Tool.
e. Did the test light illuminate for 2 seconds when the fuel pump was commanded "ON" ?
[YES] Go to Step 17.
[NO] Go to Step 14.
14. a. Reconnect the horn relay in its proper location.
b. Check for a short circuit, blown fuse or open circuit between the relay and the fuel tank.
c. Is the action complete?
[YES] Verify repair.
15. a. With the fuel pump electrical connector at the fuel tank disconnected, connect a test light between the feed wire and the ground wire (harness side).
b. Command the fuel pump "ON" with a Scan Tool.
c. Did the test light illuminate for 2 seconds?
[YES] Go to Step 18.
[NO] Go to Step 16.
16. a. Repair the open circuit in the fuel pump ground wire.
b. Is the action complete?
[YES] Verify repair.
17. a. Reconnect the horn relay in its proper location.
b. Replace the fuel pump relay.
c. Is the action complete?
[YES] Verify repair.
18. a. Replace the fuel pump.
b. Is the action complete?
[YES] Verify repair.