Component Tests and General Diagnostics

Fuel System Diagnosis (FPCM)

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit/System Description

The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in Crank or Run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank 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 is contained by the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and 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 pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The 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.

Reference Information
Description and Operation

Fuel System Description (Fuel System Description)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

* CH-48027 Digital Pressure Gauge
* J 37287 Fuel Line Shut-off Adapter

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 adequate fuel is in the fuel tank before proceeding.
* The fuel pump 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.
* DO NOT perform the Fuel System Diagnosis if the engine coolant temperature 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 beyond the pressure relief valves set point of 690 kPa = / -5 % (100 psi ±5 %).

1. Ignition OFF, all accessories OFF, install a CH-48027 . Refer to Fuel Pressure Gauge Installation and Removal (Fuel Pressure Gauge Installation and Removal).
2. Ignition ON, engine OFF, command the fuel pump ON with a scan tool. Verify the fuel pressure is between 345-690 kPa (50-100 psi) with the pump running.
3. Engine ON with the engine idling at normal operating temperature, the Fuel Rail Pressure Sensor parameter should read between 296.4-310.3 kPa (43-45 psi).

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.

1. Ignition ON, engine OFF, command the fuel pump ON with a scan tool and observe the fuel pressure gauge while the fuel pump is operating. Verify the fuel pressure is between 345-690 kPa (50-100 psi).

• If the fuel pressure is greater than the specified range, replace the fuel pump module.
• 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 fuel pump module.

* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.

2. Verify that the fuel pressure, after the fuel pump is turned off, decreases to 500-599 kPa (72-87 psi), and does not decrease more than 34 kPa (5 psi) in 1 minute from that point.

• If the fuel pressure stays above 600 kPa (87 psi), replace the fuel pump module.
• If the fuel pressure decreases more than the specified value, perform the following procedure:

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (CH-48027) (Service and Repair).
2. Install the J 37287 between the fuel feed pipe and the fuel rail.
3. Open the valve on the J 37287 .
4. Ignition ON, command the fuel pump ON with a scan tool and bleed the air from the CH-48027 .
5. Command the fuel pump ON and then OFF with a scan tool.
6. Close the valve on the J 37287 .
7. Monitor the fuel pressure for 1 minute.

• 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 fuel pump module.

3. 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 minutes.

• If the fuel pressure decreases more than the specified value, replace the fuel pump module.

4. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 . The fuel pressure should not drop off during acceleration, cruise or hard cornering.

• If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel pump module.

* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections

5. If the fuel system tests normal, refer to Symptoms - Engine Controls (Symptoms - Engine Controls).

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.