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Fuel System Diagnosis

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

When the ignition is turned ON, the engine control module (ECM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. The in-tank fuel pump remains ON as long as the engine is cranking or running and the ECM receives crankshaft reference pulses. If there are no reference pulses, the ECM turns the in-tank fuel pump OFF, 2 s after the ignition switch is turned ON or 2 s after the engine stops running. The electric fuel pump is incorporated into the modular fuel pump and sender assembly and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, also located in the modular fuel pump and sender assembly, through the fuel feed pipes, to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator, located in the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

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


• CH48027 Digital Pressure Gauge

• EN 37287 Fuel Line Shut-Off Adapters


For equivalent regional tools, refer to Special Tools .

Circuit/System Verification

Note
• Inspect the fuel system for damage or external leaks before proceeding.

• Verify that an adequate amount of 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.



1. Ignition ON, command the KR23A Fuel Pump Relay ON with a scan tool. You should hear the G12 Fuel Pump turn ON and OFF.

2. If the G12 Fuel Pump does not turn ON, refer to Fuel Pump Electrical Circuit Diagnosis .

3. Ignition OFF and all accessories off, install the CH 48027 Digital Pressure Gauge.

4. Ignition ON, command the KR23A Fuel Pump Relay ON with a scan tool. Verify the fuel pressure is between 365-414 kPa (53-60 PSI) and remains steady for 5 m.


Circuit/System Testing


1.
Note
• The KR23A Fuel Pump Relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

• Do not start the engine.


Ignition ON, engine OFF, command the KR23A Fuel Pump Relay ON with a scan tool and observe the fuel pressure gauge while the G12 Fuel Pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 PSI).

2. If the fuel pressure is greater than the specified range, replace the G12 Fuel Pump.

3. If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the G12 Fuel Pump.

• Restricted fuel feed pipe

• Restricted or clogged strainer

• Restricted or plugged fuel filter

• Inspect the G12 Fuel Pump harness connectors and the ground circuits of the fuel pump for poor connections.

4.
Note

The fuel pressure may vary slightly when the G12 Fuel Pump stops operating. After the G12 Fuel Pump stops operating, the fuel pressure should stabilize and remain constant.


Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) in 1 min.

5. If the fuel pressure decreases more than the specified value, perform the following procedure:

5.1. Ignition OFF, relieve fuel pressure.

5.2. Install the EN 37287 Fuel Line Shut-Off Adapters between the fuel feed pipe and the fuel rail.

5.3. Open the valve on the EN 37287 Fuel Line Shut-Off Adapter.

5.4. Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the digital pressure gauge.

5.5. Close the valve on the EN 37287 Fuel Line Shut-Off Adapters.

5.6. Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) in 1 minute.

5.7. If the fuel pressure decreases more than 34 kPa (5 PSI) within the specified time, locate and replace the leaking fuel injector(s).

5.8. If the fuel pressure does not decrease more than 34 kPa (5 PSI) within the specified time, replace the G12 Fuel Pump.

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

7. If the fuel pressure decreases more than the specified value, replace the G12 Fuel Pump.

8. Remove the EN 37287 Fuel Line Shut-Off Adapters and CH 48027 Digital Pressure Gauge.

9. Operate the vehicle within the conditions of the customers concern while monitoring fuel related parameters with a scan tool. The scan tool parameters should not indicate a lean condition.

10. If the scan tool parameters indicate a lean condition, test for a restricted fuel feed pipe, restricted fuel filter, or poor connections at the harness connectors and ground circuits of the fuel pump. If all test normal, replace the fuel pump.

11. If the fuel system tests normal, refer to Symptoms - Engine Controls .


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Tank Fuel Pump Module Replacement