Component Tests and General Diagnostics
Fuel System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit/System Description
The engine control module (ECM) supplies voltage to the fuel pump power control module when the ECM detects that the ignition is ON. The voltage from the ECM to the fuel pump power control module remains active for 2 s, unless the engine is in Crank or Run. While this voltage is being received, the fuel pump power control module closes the ground switch of the fuel tank fuel pump module and also supplies a varying voltage to the fuel tank fuel pump module in order to maintain the desired fuel line 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.
An electric turbine style fuel pump attaches to the fuel tank pump module inside the fuel tank. The fuel pump supplies fuel through the fuel feed pipe to the high pressure fuel pump. The high pressure fuel pump supplies fuel to a variable-pressure fuel rail. Fuel enters the combustion chamber through precision multi-hole fuel injectors. The high pressure fuel pump, fuel rail pressure, fuel injection timing, and injection duration are controlled by the engine control module (ECM).
Diagnostic Aids
Observe the Misfire Counters or perform the Fuel Injector Balance Test to help identify a leaking fuel injector.
Reference Information
Description and Operation
Fuel System Description Fuel System Description
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
J 37287 - Fuel Line Shut-Off Adapter
For equivalent regional tools, refer to Special Tools Tools and Equipment.
Circuit/System Verification
Note:
* Repair all fuel system related DTCs before performing this diagnostic.
* Inspect the fuel system for damage or external leaks before proceeding.
* Verify that adequate fuel is in the fuel tank before proceeding.
* The Fuel Pump Enable may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
* DO NOT perform the Fuel System Diagnosis if the engine coolant temperature is above 60°C (150°F). High fuel pressure readings may result due to hot soak fuel boiling. With the engine OFF, the fuel pressure may increase beyond the pressure relief regulator valve's setting point of 690 kPa (100 psi) ± 5 percent.
1. Ignition ON, engine OFF, command the Fuel Pump Enable ON several times with a scan tool.
2. Verify the Fuel Pressure Sensor parameter is between 345-650 kPa (50-94 psi) with the fuel pump running.
• If less than 345 kPa (50 psi)
1. Ignition OFF.
2. Verify none of the conditions below exist:
* Restricted fuel feed pipe
* Poor connections at the fuel pump harness connector and the ground circuits
• If a condition exists
Repair as necessary
• If none of the conditions exist
Test or replace the G12 Fuel Pump
• If greater than 650 kPa (94 psi)
Replace the G12 Fuel Pump
• If between 345-650 kPa (50-94 psi)
3. Verify that the 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 Fuel Pressure Sensor parameter does not decrease greater than 34 kPa (5 psi) in 1 minute.
• If the fuel pressure decreases greater than 34 kPa (5 psi)
1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief Service and Repair.
2. Install the J 37287 - Adapter between the chassis fuel feed hose and the high pressure fuel pump.
3. Open the valve on the J 37287 - Adapter.
4. Ignition ON, command the Fuel Pump Enable ON and then OFF with a scan tool.
5. Close the valve on the J 37287 - Adapter.
6. Verify that the Fuel Pressure Sensor parameter does not decrease greater than 34 kPa (5 psi) in 1 minute.
• If the fuel pressure drops
Test or replace the G12 Fuel Pump
• If the fuel pressure does not drop
Locate and replace the leaking Q17 Fuel Injector
• If the fuel pressure does not decrease greater than 34 kPa (5 psi)
5. Operate the vehicle within the conditions of the customer's concern while monitoring the Fuel Pressure Sensor parameter with a scan tool.
6. Verify the Fuel Pressure Sensor parameter does not drop off during acceleration, cruise, or hard cornering.
• If the fuel pressure drops off
1. Ignition OFF.
2. Verify none of the conditions below exist:
* Restricted fuel feed pipe
* Poor connections at the fuel pump harness connector and the ground circuits
• If a condition exists
Repair as necessary
• If none of the conditions exist
Test or replace the G12 Fuel Pump
• If the fuel pressure does not drop off
7. If the fuel system components test normal, refer to Symptoms - Engine Controls Symptoms - Engine Controls , Fuel Injector Solenoid Coil Test Fuel Injector Solenoid Coil Test , and Fuel Injector Balance Test Fuel Injector Balance Test for further diagnosis.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Fuel Feed Front Pipe Replacement (LCV) Fuel Feed Front Pipe ReplacementFuel Feed Front Pipe Replacement (LTG) Fuel Feed Front Pipe Replacement
* Fuel Feed Pipe Replacement (At Tank) Fuel Feed Pipe Replacement (At Tank)Fuel Feed Pipe Replacement (Engine to Chassis LCV) Fuel Feed Pipe Replacement (Engine to Chassis)Fuel Feed Pipe Replacement (Engine to Chassis LTG) Fuel Feed Pipe Replacement (Engine to Chassis)
* Fuel Injector Replacement Service and Repair
* Fuel Tank Fuel Pump Module Replacement (NT7) Fuel Tank Fuel Pump Module Replacement (NT7)Fuel Tank Fuel Pump Module Replacement (NU6) Fuel Tank Fuel Pump Module Replacement (NU6)