Cobalt L4-2.2L (2008)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Instructions
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions provide an overview of each diagnostic category.
Circuit/System Description
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2
seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition
reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the
ignition remains ON.
The fuel tank stores the fuel supply. The electric fuel pump supplies fuel through a fuel filter located in the fuel tank to the fuel injection system. The
pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator, located in the fuel tank, maintains the
correct fuel pressure to the fuel injection system.
Special Tools
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CH-48027 Digital Pressure Gage
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J37287 Fuel Line Shut-Off Adapter
Circuit/System Verification
Important:
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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 relay 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.
1. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.
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If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis. See: Computers and Control Systems/Testing and
Inspection/Component Tests and General Diagnostics
2. Ignition OFF, all accessories OFF, install a CH-48027.
3. Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and
does not decrease more than 34 kPa (5 psi) in 1 minute.
Circuit/System Testing
Important:
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The fuel pump relay 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.
Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating.
Verify the fuel pressure is between 345-414 kPa (50-60 psi).
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If the fuel pressure is greater than the specified range, replace the fuel pump fuel reservoir pump fuel strainer orifice.
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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 fuel
pump and the fuel pump fuel reservoir pump fuel strainer orifice.
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Restricted fuel feed pipe
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Restricted or plugged fuel filter
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Restricted or plugged strainer