Chevrolet Trax: Fuel system diagnosis (LUV)

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 chassis control module when the ECM detects that the ignition is ON. The voltage from the ECM to the chassis control module remains active for 2 s, unless the engine is in Crank or Run. While this voltage is being received, the chassis 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 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.

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

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 (LUJ) , Fuel System Description (LUV)

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

• CH 48027 Digital Pressure Gauge
• EN 37287 Fuel Line Shut-off Adapter

For equivalent regional tools, refer to Special Tools (Diagnostic 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.
• Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.

1. Ignition OFF, all accessories OFF, install a CH 48027 Gauge.

NOTE: 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) +- 5 percent.

2. Ignition ON, engine OFF, command the Fuel Pump Enable On several times with a scan tool.
3. Verify the fuel pressure is between 345-650 kPa (50-94 psi) with the fuel pump running.

• 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)

4. Verify that the fuel pressure decreases to less than 600 kPa (87 psi) after the fuel pump is turned off.

• If greater than 600 kPa (87 psi)

Replace the G12 Fuel Pump.

• If less than 600 kPa (87 psi)

5. Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.

• If greater than 34 kPa (5 psi)

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

• If less than 34 kPa (5 psi)

6. Relieve the fuel pressure to 69 kPa (10 psi).
7. Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 min.

• If greater than 14 kPa (2 psi)

Replace the G12 Fuel Pump.

• If less than 14 kPa (2 psi)

8. Engine idling.
9. Verify the Chassis Control Module 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)

10. 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 Circuit/System Testing - Fuel Pressure Low.

• If less than 1.5

11. Verify 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)

12. If the fuel system components test normal, refer to Symptoms - Engine Controls, and Fuel Injector 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.

• If no conditions exist

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 engine compartment fuel feed pipe.
3. Open the valve on the EN 37287 Adapter.
4. Ignition ON, command the Fuel Pump Enable On with a scan tool and bleed the air from the CH 48027 Gauge.
5. Command the Fuel Pump Enable On and then Off with a scan tool.
6. Close the valve on the EN 37287 Adapter.
7. Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 min.

• If greater than 34 kPa (5 psi)

Locate and replace the leaking Q17 Fuel Injector.

• If less than 34 kPa (5 psi)

Replace the G12 Fuel Pump.

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.

• If no conditions exist

Replace the G12 Fuel Pump.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Fuel Feed Pipe Replacement (Engine to Tank) , Fuel Feed Pipe Replacement (At Tank AWD) , Fuel Feed Pipe Replacement (At Tank FWD)
• Fuel Injector Replacement
• Fuel Tank Fuel Pump Module Replacement (AWD) , Fuel Tank Fuel Pump Module Replacement (FWD)

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