Sierra 1500 4WD V8-6.0L (2007)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis (FPCM)
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 engine control module (ECM) supplies a high voltage signal to the fuel pump flow control module (FPCM) when the ECM detects that the ignition
is on. The high voltage signal from the ECM to the FPCM remains active for two seconds, unless the engine is in crank or run. While this signal 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.
Circuit/System Verification
Important:
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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 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.
Ignition ON, command the fuel pump ON with a scan tool. You should hear the fuel pump turn ON and OFF.
‹› If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis (with LMG, LC9, or LY6) Fuel Pump Electrical Circuit
Diagnosis (FPCM). See: Powertrain Management/Computers and Control Systems/Testing and Inspection/Component Tests and General
Diagnostics See: Powertrain Management/Computers and Control Systems/Testing and Inspection/Component Tests and General Diagnostics
1. Ignition OFF, all accessories OFF, install the CH-48027. Refer to Fuel Pressure Gage Installation and Removal. See: Fuel Pressure Gage
Installation and Removal
2. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and remains steady
for 5 minutes.
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, 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).
‹› If the fuel pressure is greater than the specified range, replace the fuel pump.
‹› If the fuel pressure is less than the specified range, remove the fuel tank and test, inspect, and repair the items listed below. If all items test
normal, replace the fuel pump.
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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
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Stuck or binding fuel level float
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Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel
pressure should stabilize and remain constant.
