Fuel System Diagnosis (LAU Except China)
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Fuel System Diagnosis (LAU Except China)
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Circuit/System Description
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The engine control module (ECM) supplies voltage to the fuel pump control module when the ECM detects that the ignition is ON. The voltage from the ECM to the fuel pump control module remains active for two seconds, unless the engine is in Crank or Run. While this voltage is being received, the fuel pump control module closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank 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.
An electric turbine style fuel pump attaches to the primary fuel tank module inside the fuel tank. The fuel pump supplies fuel through the fuel filter, contained in the fuel tank module, and the fuel feed pipe to the fuel injection system. The primary 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.
The primary fuel tank module also contains a primary jet pump and a secondary jet pump. Fuel pump flow loss, caused by vapor expulsion in the pump inlet chamber, is diverted to the primary jet pump and the secondary jet pump through a restrictive orifice located on the pump cover. The primary jet pump fills the reservoir of the primary fuel tank module. The secondary jet pump creates a venturi action which causes the fuel to be drawn from the secondary side of the fuel tank, through the fuel transfer pipe, to the primary side of the fuel tank.
Description and Operation
Fuel System Description (LF1)
Fuel System Description (LAU or LY7)
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
Special Tools
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CH48027
Digital Pressure Gauge
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J37287
Fuel Line Shut-Off Adapter
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Circuit/System Verification
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Note
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Repair all fuel system related DTCs before performing this diagnostic.
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Inspect the fuel system for damage or external leaks before proceeding.
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Verify that adequate fuel is in the fuel tank before proceeding.
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The Fuel Pump Enable may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
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Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.
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2.
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Note
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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 regulator valve's setting point of 690 kPa (100 psi) ± 5 percent.
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Ignition ON, engine OFF, command the Fuel Pump Enable ON with a scan tool. Verify the fuel pressure is between 345-690 kPa (50-100 psi) with the fuel pump running.
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3.
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Engine idling at normal operating temperature, the Fuel Pump Flow Control Module Fuel Pressure Sensor parameter should read between 300-400 kPa (43-58 psi).
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1.
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Note
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The Fuel Pump Enable may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
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DO NOT start the engine.
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Ignition ON, engine OFF, command the Fuel Pump Enable 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).
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2.
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If the fuel pressure is greater than the specified range, replace the primary fuel tank module.
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3.
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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 primary fuel tank module.
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Restricted fuel feed pipe
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Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
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4.
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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.
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5.
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If the fuel pressure stays above 600 kPa (87 psi), replace the primary fuel tank module.
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6.
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If the fuel pressure decreases more than the specified value, perform the following procedure:
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6.2.
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Install the
J 37287
Adapter between the chassis fuel feed hose and the engine compartment fuel feed pipe.
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6.3.
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Open the valve on the
J 37287
Adapter.
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6.4.
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Ignition ON, command the Fuel Pump Enable ON with a scan tool and bleed the air from the
CH 48027
Gauge.
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6.5.
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Command the Fuel Pump Enable ON and then OFF with a scan tool.
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6.6.
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Close the valve on the
J 37287
Adapter.
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6.7.
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Monitor the fuel pressure for 1 min.
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6.8.
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If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s).
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6.9.
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If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the primary fuel tank module.
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7.
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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.
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8.
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If the fuel pressure decreases more than the specified value, replace the primary fuel tank module.
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9.
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Run the car within conditions for the customer's problem while monitoring the fuel pressure with the gauge
CH 48027
. The fuel pressure should not drop when accelerating, cruising, or tight cornering.
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10.
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If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the primary fuel tank module.
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Restricted fuel feed pipe
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Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
