Fuel System Diagnosis
Diagnostic Instructions
Circuit/System Description
The engine control module (ECM) supplies a high voltage signal to the fuel pump flow control module when the ECM detects that the ignition is ON. The high voltage signal from the ECM to the fuel pump flow control module remains active for 2 s, unless the engine is in Crank or Run. While this signal is being received, the fuel pump flow 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 rail 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 module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, contained in the fuel tank module, and 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 venturi pump located on the bottom of the fuel tank module. The function of the venturi pump is to fill the fuel tank module reservoir. The fuel tank 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.
Reference Information
Description and Operation
Fuel System Description
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Special Tools
| • | CH 48027 Digital Pressure Gauge |
| • | EN 37287 Fuel Line Shut-Off Adapters |
For equivalent regional tools, refer to Special Tools .
Circuit/System Verification
Note:
| • | Repair all fuel system related DTCs before performing this diagnostic, unless instructed here from a DTC diagnostic. |
| • | 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. |
| • | Before proceeding with this test review the User Manual of the CH 48027 Digital Pressure Gauge chapter 5 for Safety Information and Instructions. |
| • | Do not perform the Fuel System Diagnosis if the engine coolant temperature (ECT) 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 to the setting of the pressure relief regulator valve, 580 kPa (84 PSI). |
- Ignition OFF, all accessories OFF, install a CH 48027 Digital Pressure Gage.
- Ignition ON, engine OFF, command the fuel pump ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 PSI) and does not decrease greater than 34 kPa (5 PSI) in 1 min.
Circuit/System Testing
Note:
| • | The fuel pump 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 fuel pump 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).
| ⇒ | 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. |
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 stabilise and remain constant.
- Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) in 1 min.
| ⇒ | If the fuel pressure decreases more than the specified value, perform the following procedure: |
| 2.1. | Ignition OFF, relieve fuel pressure. |
| 2.2. | Install the EN 37287 Fuel Line Shut-Off Adapters between the fuel feed pipe and the fuel rail. |
| 2.3. | Open the valve on the EN 37287 Fuel Line Shut-Off Adapters. |
| 2.4. | Ignition ON, command the fuel pump ON with a scan tool and bleed the air from the digital pressure gauge. |
| 2.5. | Close the valve on the EN 37287 Fuel Line Shut-Off Adapters. |
| 2.6. | Command the fuel pump ON with a scan tool. |
| 2.7. | Verify the fuel pressure does not decrease greater than 34 kPa (5 PSI) in 1 min. |
| ⇒ | If the fuel pressure decreases more than 34 kPa (5 PSI) within the specified time, locate and replace the leaking fuel injector(s). |
| ⇒ | If the fuel pressure does not decrease more than 34 kPa (5 PSI) within the specified time, replace the G12 Fuel Pump. |
- 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.
| ⇒ | If the fuel pressure decreases more than the specified value, replace the G12 Fuel Pump. |
- Remove the EN 37287 Fuel Line Shut-Off Adapters and CH 48027 Digital Pressure Gauge.
- 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.
| ⇒ | 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. |
- 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
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