Chevrolet Trax: Fuel system diagnosis (LUJ)

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) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The ECM continues to enable the fuel pump relay as long as ignition reference pulses are detected. The ECM disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

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 provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a jet pump located in the fuel tank fuel pump module. The function of the jet pump is to fill the fuel tank fuel pump module reservoir. The fuel pressure regulator, attached to the fuel rail, maintains the correct fuel pressure to the fuel injection system. The fuel return pipe returns unused fuel to the fuel tank. The fuel tank fuel pump module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times

Reference Information

Description and Operation

Engine Controls Schematics (Encore) , Engine Controls Schematics (Trax)

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 41769 Fuel Line Quick Disconnect Tool
• CH 48027 Digital Pressure Gauge
• EN 37287 Fuel Line Shut-off Adapters

For equivalent regional tools, refer to Special Tools (Diagnostic Tools) .

Circuit/System Verification

NOTE:

• 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 Relay 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 ON.
2. Verify that the fuel pump turns ON and OFF when commanding the Fuel Pump Relay On and Off with a scan tool.

• If the fuel pump does not turn ON and OFF

Refer to Fuel Pump Electrical Circuit Diagnosis (LUJ).

• If the fuel pump does turn ON and OFF

3. Ignition OFF, all accessories OFF, install a CH 48027 Gauge.
4. Ignition ON, engine OFF.
5. Command the Fuel Pump Relay On several times with a scan tool.
6. Verify the fuel pressure is between 276-345 kPa (40-50 psi) with the fuel pump running.

• If less than 276 kPa (40 psi)

Refer to Circuit/System Testing - Fuel Pressure Low.

• If greater than 345 kPa (50 psi)

Refer to Circuit/System Testing - Fuel Pressure High.

• If between 276-345 kPa (40-50 psi)

7. 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)

8. Relieve the fuel pressure to 69 kPa (10 psi).
9. 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)

10. Engine idling, verify the fuel pressure decreases 21-69 kPa (3-10 psi) from the pressure noted in Step 6.

• If the fuel pressure does not decrease

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

• If the fuel pressure decreases

11. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH 48027 Gauge.
12. 12. Verify the fuel pressure does not drop off during acceleration, cruise or hard cornering.

• If the fuel pressure drops off

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

• If the fuel pressure does not drop off

13. 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

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

CAUTION: Do not connect the Fuel Line Shut-off Adapters directly at the fuel rail. The Fuel Line Quick Disconnect Tools will not work at this location. Damage could occur to the fuel rail.

3. Install the EN 37287 Adapter between the metal chassis fuel return pipe and the nylon engine compartment fuel return pipe.
4. Open the valve on the EN 37287 Adapter.
5. Ignition ON, command the Fuel Pump Relay On with a scan tool and bleed the air from the CH 48027 Gauge.

NOTE: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi).

6. Slowly close the valve on the EN 37287 Adapter. while commanding the Fuel Pump Relay On with a scan tool.
7. Verify that the fuel pressure increases to greater than 345 kPa (50 psi).

• If less than 345 kPa (50 psi)

Replace the G12 Fuel Pump.

• If greater than 345 kPa (50 psi)

Replace the Q18 Fuel Pressure Regulator.

Fuel Pressure High

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief .
2. Disconnect the fuel return pipe at the fuel rail.
3. Attach a length of flexible fuel hose to the fuel rail return pipe.
4. Place the open end of the flexible fuel hose into an approved gasoline container.
5. Ignition ON, command the Fuel Pump Relay On with a scan tool.
6. Verify the fuel pressure is between 276-345 kPa (40-50 psi) with the fuel pump running.

• If less than 345 kPa (50 psi)

Locate and replace the restricted fuel return pipe.

• If greater than 345 kPa (50 psi)

7. Verify none of the conditions listed below exist:

• Restricted fuel rail return pipe
• Restricted fuel rail outlet passage
• If a condition exists

Repair as necessary.

• If no conditions exist

Replace the Q18 Fuel Pressure Regulator.

Fuel Pressure Leaks Down

1. Disconnect the fuel pressure regulator vacuum hose.
2. Engine idling, apply 12-14 inches of vacuum to the fuel pressure regulator with a hand held vacuum pump and verify the fuel pressure decreases 21-69 kPa (3-10 psi).

• If the fuel pressure does not decrease

Replace the fuel pressure regulator.

• If the fuel pressure decreases

3. Ignition OFF, verify none of the conditions below exist:

• Damaged, leaking, or restricted fuel pressure regulator hose
• Restricted vacuum source
• If a condition exists

Repair as necessary.

• If no conditions exist

4. Ignition ON, command the Fuel Pump Relay On with a scan tool and inspect for a fuel leak from the fuel pressure regulator vacuum port.

• If there is a fuel leak

Replace the fuel pressure regulator.

• If there is no fuel leak

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

CAUTION: Do not connect the Fuel Line Shut-off Adapters directly at the fuel rail. The Fuel Line Quick Disconnect Tools will not work at this location. Damage could occur to the fuel rail.

6. Install the EN 37287 Adapters between the metal chassis fuel pipes and the nylon engine compartment fuel pipes.
7. Open the valves on the EN 37287 Adapters.
8. Ignition ON, command the Fuel Pump Relay On with a scan tool and bleed the air from the CH 48027 Gauge.
9. Command the Fuel Pump Relay On and then Off with a scan tool.
10. Close the valve on the fuel feed pipe EN 37287 Adapter.
11. Monitor the CH 48027 Gauge for 1 minute and verify that the fuel pressure does not decrease.

• If the fuel pressure does not decrease

Replace the G12 Fuel Pump.

• If the fuel pressure decreases

12. Ignition OFF, open the valve on the fuel feed pipe EN 37287 Adapter.
13. Ignition ON, command the Fuel Pump Relay On and then Off with a scan tool.
14. Close the valve on the fuel return pipe EN 37287 Adapter.
15. Monitor the CH 48027 Gauge for 1 minute and verify that the fuel pressure does not decrease.

• If the fuel pressure does not decrease

Replace the Q18 Fuel Pressure Regulator.

• If the fuel pressure decreases

Locate and replace the leaking Q17 Fuel Injector.

Fuel Pressure Drops Off

1. Disconnect the fuel pressure regulator vacuum hose.
2. Engine idling, apply 12-14 inches of vacuum to the fuel pressure regulator with a hand held vacuum pump and verify the fuel pressure decreases 21-69 kPa (3-10 psi).

• If the fuel pressure does not decrease

Replace the fuel pressure regulator.

• If the fuel pressure decreases

3. Ignition OFF, verify none of the conditions below exist:

• Damaged, leaking, or restricted fuel pressure regulator hose
• Restricted vacuum source
• If a condition exists

Repair as necessary.

• If no conditions exist

4. Ignition ON, command the Fuel Pump Relay On with a scan tool and inspect for a fuel leak from the fuel pressure regulator vacuum port.

• If there is a fuel leak

Replace the fuel pressure regulator.

• If there is no fuel leak

5. 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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