• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The engine control module (ECM) supplies voltage to the fuel pump driver control module when the ECM detects that the ignition is ON. The voltage signal from the ECM to the fuel pump driver control module remains active for 2 s, unless the engine is in Crank or Run. While this voltage is being received, the fuel pump driver control module closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank fuel pump module in order to maintain the desired fuel rail pressure.

The fuel system is an electronic returnless on-demand design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel tank fuel pump module inside the fuel tank. The fuel pump supplies fuel through the fuel feed pipe and the fuel feed front pipe check valve to the high pressure fuel pump. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel tank fuel pump module. The function of the venturi pump is to fill the fuel tank fuel pump module reservoir. The fuel tank fuel pump module contains a reverse flow check valve. Both check valves maintain fuel pressure in the fuel feed pipe in order to prevent long cranking times.

• Observe the scan tool Misfire Counters or perform the Fuel Injector Balance Test to help identify a leaking fuel injector.
• A faulty component may cause the following noises:Damper located in the fuel feed pipe—Buzz/Knock/Rattle/Tick@600 to 800 RPM
• A faulty damper located in the fuel feed pipe may cause DTC P2635 or P3188 to set.
• An erratic low side fuel pressure leak-down reading may be caused by air/vapor in the fuel feed line, which can be caused by the following:
• Ambient conditions
• Engine operating conditions—Cold Start-Up/Warm/Hot
• Fuel Alcohol Content
• Fuel blend—Summer/Winter
• Fuel octane rating

Fuel System Description

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

• CH-41769 Fuel Line Quick Disconnect Tool
• EN-37287 Fuel Line Shut-off Adapter

For equivalent regional tools, refer to Special Tools.

1. Ignition ON, engine OFF, command the Fuel Pump Enable On several times with a scan tool.
2. Verify that the scan tool Fuel Pressure Sensor parameter is between 345–650 kPa (50–94 PSI).
• If less than 345 kPa (50 PSI)

  Refer to Circuit/System Testing - Fuel Pressure Low.

• If greater than 650 kPa (94 PSI)

  Replace the G12 Fuel Pump.

• If between 345–650 kPa (50–94 PSI)
3. Verify that the scan tool Fuel Pressure Sensor parameter, after the fuel pump is turned off, decreases to less than 600 kPa (87 PSI).
• If greater than 600 kPa (87 PSI)

  Replace the G12 Fuel Pump

• If less than 600 kPa (87 PSI)
4. Verify that the scan tool Fuel Pressure Sensor parameter does not decrease greater than 34 kPa (5 PSI) in 1 min.
• If greater than 34 kPa (5 PSI)

  Refer to Circuit/System Testing - Fuel Pressure Leaks Down.

• If less than 34 kPa (5 PSI)
5. Engine idling.
6. Verify that the scan tool Fuel Pressure Sensor parameter is between 300–400 kPa (43–58 PSI).
• If less than 300 kPa (43 PSI)

  Refer to Circuit/System Testing - Fuel Pressure Low.

• If greater than 400 kPa (58 PSI)

  Replace the G12 Fuel Pump.

• If between 300–400 kPa (43–58 PSI)
7. Verify that the scan tool Fuel Pressure Sensor and the Desired Fuel Pressure are within 45 kPa (6.5 PSI) at 300 kPa (43.5 PSI) request or 60 kPa (8.7 PSI) at 400 kPa (58 PSI) request of each other while operating the vehicle through varying loads.
• If greater than 45 kPa (6.5 PSI) / 60 kPa (8.7 PSI)

  Refer to Circuit/System Testing - Fuel Pressure Drops Off.

• If less than 45 kPa (6.5 PSI) / 60 kPa (8.7 PSI)
8. If the fuel system components test normal, refer to Symptoms - Engine Controls and Fuel Injector Diagnosis.

1. Verify none of the conditions listed below exist:
• Restricted or dislocated fuel feed front pipe check valve
• Restricted fuel feed pipe
• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
• If a condition exists

  Repair as necessary.

• If no conditions exist

  Replace the G12 Fuel Pump.

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief.
2. Install the EN-37287 between the chassis fuel feed hose and the engine compartment fuel feed pipe.
3. Open the valve on the EN-37287 .
4. Ignition ON, command the Fuel Pump Enable On and then Off with a scan tool.
5. Close the valve on the EN-37287 .
6. Verify that the scan tool Fuel Pressure Sensor parameter does not decrease more than 34 kPa (5 PSI) in 1 min.
• If greater than 34 kPa (5 PSI)

  Replace the G12 Fuel Pump.

• If less than 34 kPa (5 PSI)
7. Test for a faulty fuel feed front pipe check valve.
• If a condition exists

  Replace the fuel feed front pipe.

• If no condition exists
8. Test for a leaking G18 High Pressure Fuel Pump.
• If a condition exists

  Replace the G18 High Pressure Fuel Pump.

• If no condition exists

  Locate and replace the leaking Q17 Fuel Injector.

1. Verify none of the conditions listed below exist:
• Restricted or dislocated fuel feed front pipe check valve
• Restricted fuel feed pipe
• Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
• If a condition exists

  Repair as necessary.

• If no conditions exist

  Replace the G12 Fuel Pump.

Perform the Diagnostic Repair Verification after completing the repair.

• Fuel Feed Front Pipe Replacement
• Fuel Feed Pipe Replacement
• Fuel Feed Intermediate Pipe Replacement
• Fuel Injector Replacement
• Fuel Pump Replacement for G18 High Pressure Fuel Pump replacement
• Fuel Tank Fuel Pump Module Replacement