Buick Regal: Fuel System Diagnosis

Diagnostic Instructions

• 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.

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

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information

Special Tools

EN 37287 Fuel Line Shut-Off Adapter

For equivalent regional tools, refer to Special Tools (Diagnostic Tools) and Special Tools (Mechanical 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 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 60ºC (150ºF). 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) ÂÂ+- 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)

Refer to Fuel Pressure Low in Circuit/System Testing.

• If greater than 650 kPa (94 psi)

Replace the G12 Fuel Pump.

• Go to next step: 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.

• Go to next step: 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 greater than 34 kPa (5 psi)

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

• Go to next step: If less than 34 kPa (5 psi)

5. Engine idling.

6. Verify the Fuel Pressure Sensor parameter is between 300 - 400 kPa (43 - 58 psi).

• If less than 300 kPa (43 psi)

Refer to Fuel Pressure Low in Circuit/System Testing.

• If greater than 400 kPa (58 psi)

Replace the G12 Fuel Pump.

• Go to next step: If between 300 - 400 kPa (43 - 58 psi)

7. Verify the scan tool Short Term Fuel Pump Trim and the Long Term Fuel Pump Trim when multiplied together are less than 1.5.

• If greater than 1.5

Refer to Fuel Pressure Low in Circuit/System Testing.

• Go to next step: If less than 1.5

8. Verify the scan tool 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 Fuel Pressure Drops Off in Circuit/System Testing.

• Go to next step: If less than 45 kPa (6.5 psi)/60 kPa (8.7 psi)

9. If the fuel system components test normal, refer to Symptoms - Engine Controls and Fuel Injector Diagnosis for further diagnosis.

Circuit/System Testing

Fuel Pressure Low

1. Verify none of the conditions listed below exist:

• 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.

• Go to next step: If no conditions exist

Go to next step: Replace the G12 Fuel Pump.

Fuel Pressure Leaks Down

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief.

2. Install the EN 37287 Adapter between the chassis fuel feed hose and the high pressure fuel pump.

3. Open the valve on the EN 37287 Adapter.

4. Ignition ON, command the Fuel Pump Enable On and then Off with a scan tool.

5. Close the valve on the EN 37287 Adapter.

6. Verify that the Fuel Pressure Sensor parameter does not decrease greater than 34 kPa (5 psi) in 1 minute.

• If greater than 34 kPa (5 psi)

Replace the G12 Fuel Pump.

• Go to next step: If less than 34 kPa (5 psi)

Fuel Pressure Drops Off

1. Verify none of the conditions listed below exist:

• 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.

• Go to next step: If no conditions exist

Go to next step: Replace the G12 Fuel Pump.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Fuel Feed Front Pipe Replacement
• Fuel Injector Replacement
• Fuel Tank Fuel Pump Module Replacement (FWD) or Fuel Tank Fuel Pump Module
• Replacement (AWD)

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