Fuel System Diagnosis
Diagnostic InstructionsCircuit/System Description

For an overview of the component/system, refer to:Fuel System Description

Component

Description

A7 Fuel Pump and Level Sensor Assembly

The fuel pump has a DC motor that is controlled by a PWM signal to achieve the desired fuel pressure.

K111 Fuel Pump Driver Control Module

The control module K111 supplies the fuel pump with a PWM signal in order to achieve the desired fuel line pressure.

Q17 Fuel Injector

Fuel injectors are solenoid valves that inject fuel either into the intake system or directly into the cylinder. The amount of fuel injected depends on the length of the electrical pulse that is applied.The fuel injectors of this system have an operating voltage of 12 V.

Q18 Fuel Pressure Regulator

Q18 is part of the component:G18 High Pressure Fuel Pump

The fuel pressure regulator is a diaphragm relief valve. The diaphragm has fuel pressure on one side and regulator spring pressure on the other side.The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system.The fuel pressure regulator delivers the needed fuel to the fuel rail. The unused fuel drops back into the reservoir of the fuel tank fuel pump module.The fuel pressure regulator is not vacuum biased.The fuel pressure regulator maintains fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Fuel Pump Check Valve

The one-way check valve is part of the component:G12 Fuel Pump

The check valve maintains pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Diagnostic Aids
  • 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
Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Master Electrical Component List

Electrical Information ReferenceScan Tool Reference

Control Module References

Special Tools
  • CH-41769 - Fuel Line Quick Disconnect Tool
  • EN-37287 - Fuel Line Shut-Off Adapter

Equivalent regional tools:Refer to:Special Tools

Circuit/System Verification

Note:

  • Repair all fuel system related DTCs, except P2635, before performing this diagnostic.
  • Inspect the fuel system for damage or external leaks before proceeding.
  • Verify the fuel tank is not empty before proceeding.
  • The fuel pump 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) ± <p05>%.

  1. Ignition » On / Vehicle » In Service Mode & Engine » Off
  2. Perform the scan tool control function:Fuel Pump Enable»On—Command the function On several times.

    Verify the scan tool parameter:Fuel Pressure Sensor=345 to 650 kPa (50 to 94 PSI)—While the fuel pump is running.

    • If less than 345 kPa (50 PSI)

      Refer to: Circuit/System Testing—Fuel Pressure Low

    • If greater than 650 kPa (94 PSI)

      Test or replace the component:A7 Fuel Pump and Level Sensor Assembly

    • If between 345 and 650 kPa (50 and 94 PSI)
  3. Verify the scan tool parameter:Fuel Pressure Sensor=Pressure should decrease to less than 600 kPa (87 PSI) after the fuel pump is turned Off.
    • If greater than 600 kPa (87 PSI)

      Test or replace the component:A7 Fuel Pump and Level Sensor Assembly

    • If less than 600 kPa (87 PSI)
  4. Verify the scan tool parameter:Fuel Pressure Sensor=Pressure drops less than 34 kPa (5 PSI) within 1 min.
    • If the pressure drops 34 kPa (5 PSI) or greater

      Refer to: Circuit/System Testing—Fuel Pressure Leaks Down

    • If the pressure drops less than 34 kPa (5 PSI)
  5. Ignition On - Engine Running
  6. Verify the scan tool parameter:Fuel Pressure Sensor=300 to 400 kPa (43 to 58 PSI)
    • If less than 300 kPa (43 PSI)

      Refer to: Circuit/System Testing—Fuel Pressure Low

    • If greater than 400 kPa (58 PSI)

      Test or replace the component:A7 Fuel Pump and Level Sensor Assembly

    • If between 300 and 400 kPa (43 and 58 PSI)
  7. Perform the scan tool control function:Fuel Pressure»Increase—300 kPa (43.5 PSI)

    The pressure should not drop off during acceleration, cruise or hard cornering.

  8. Verify the following parameters are within 45 kPa (6.5 PSI) of each other:
    • Desired Fuel Pressure
    • Fuel Pressure Sensor
    • If greater than 45 kPa (6.5 PSI)

      Refer to: Circuit/System Testing—Fuel Pressure Drops Off

    • If less than 45 kPa (6.5 PSI)
  9. Perform the scan tool control function:Fuel Pressure»Increase—400 kPa (58 PSI)

    The pressure should not drop off during acceleration, cruise or hard cornering.

  10. Verify the following parameters are within 60 kPa (8.7 PSI) of each other:
    • Desired Fuel Pressure
    • Fuel Pressure Sensor
    • If greater than 60 kPa (8.7 PSI)

      Refer to: Circuit/System Testing—Fuel Pressure Drops Off

    • If less than 60 kPa (8.7 PSI)
  11. Perform the following procedure/test:Fuel Injector Diagnosis

    Verify the procedure/test passes.

    • If the procedure/test does not pass

      Replace the component that failed the test:Q17 Fuel Injector

    • If the procedure/test passes
  12. Refer to:Symptoms - Engine Controls
Circuit/System TestingFuel Pressure Low
  1. Verify the following conditions do not exist:
    • Poor component electrical connections:Fuel Pump—Chassis Ground
    • Poor component electrical connections:Fuel Pump—Electrical Connector
    • Fuel Feed Pipe—Leaking/Restricted/Visible Damage
    • If a condition exists

      Repair as necessary

    • If no conditions exist
  2. Test or replace the component:A7 Fuel Pump and Level Sensor Assembly
Fuel Pressure Leaks Down
  1. Ignition/Vehicle » Off
  2. Relieve the fuel system pressure.»Refer to:Fuel Pressure Relief
  3. Install the special tool:EN-37287 - Fuel Line Shut-Off Adapter@Fuel Feed Pipe
  4. Open the valve on the tool:EN-37287 - Fuel Line Shut-Off Adapter
  5. Ignition » On / Vehicle » In Service Mode & Engine » Off
  6. Perform the scan tool control function:Fuel Pump Enable»On and Off
  7. Close the valve on the tool:EN-37287 - Fuel Line Shut-Off Adapter
  8. Verify the scan tool parameter:Fuel Pressure Sensor=Pressure drops less than 34 kPa (5 PSI) within 1 min.
    • If the pressure drops 34 kPa (5 PSI) or greater

      Locate and replace the leaking component:Q17 Fuel Injector

    • If the pressure drops less than 34 kPa (5 PSI)
  9. Test or replace the component:A7 Fuel Pump and Level Sensor Assembly
Fuel Pressure Drops Off
  1. Verify the condition does not exist:
    • Poor component electrical connections:Fuel Pump—Chassis Ground
    • Poor component electrical connections:Fuel Pump—Electrical Connector
    • Fuel Feed Pipe—Leaking/Restricted/Visible Damage
    • If a condition exists

      Repair as necessary

    • If no conditions exist
  2. Test or replace the component:A7 Fuel Pump and Level Sensor Assembly
Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair:Diagnostic Repair Verification