Fuel System Diagnosis (FPCM)
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 Control Module References 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.
* 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 the CH-48027 - Digital Pressure Gauge. Refer to Fuel Pressure Gauge Installation and Removal Testing and Inspection.
2. Ignition ON, engine OFF, command the FPCM 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 idling at the normal operating temperature, Verify the FPCM scan tool Fuel Rail Pressure Sensor parameter is between 296-310 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 FPCM 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 tank 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 tank fuel pump module.
* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
2. After the fuel pump is turned OFF, verify the fuel pressure stabilizes between 500-599 kPa (72-87 psi).
• If greater than the specified range, replace the fuel tank fuel pump module.
3. After the fuel pump is turned OFF, verify the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.
• If the pressure decreases more than the specified value, perform the following procedure:
1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (Without CH-48027) Fuel Pressure Relief (Without CH-48027)Fuel Pressure Relief (CH-48027) Fuel Pressure Relief (CH-48027).
2. Install the J 37287 - Fuel Line Shut-off Adapter between the fuel feed pipe and the fuel rail.
3. Open the valve on the J 37287 - Fuel Line Shut-off Adapter.
4. Ignition ON, command the FPCM Fuel Pump ON with a scan tool and bleed the air from the CH-48027 - Digital Pressure Gauge.
5. Command the FPCM Fuel Pump ON and then OFF with a scan tool.
6. Close the valve on the J 37287 - Fuel Line Shut-off Adapter.
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 tank fuel pump module.
4. 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 tank fuel pump module.
5. Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 - Digital Pressure Gauge. 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 tank fuel pump module.
* Restricted fuel feed pipe
* Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
6. 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.
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