H2 V8-6.2L (2008)
Fuel Pressure: Testing and Inspection
Fuel System Diagnosis
Fuel System Diagnosis
Diagnostic Instructions
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Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
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Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
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Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure Instructions)
provides an overview of each diagnostic category.
Circuit/System Description
The engine control module (ECM) supplies a high voltage signal to the fuel pump 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 2 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.
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel pump module, eliminating the need for a return pipe
from the engine. 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 attaches to 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 provides fuel at a higher rate of flow than is
needed by 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 pressure regulator, a part of the fuel pump module, maintains the correct fuel
pressure to the fuel injection system. The fuel pump module contains a reverse flow check valve. The check valve and the fuel pressure regulator
maintain 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 (See: Powertrain Management/Computers and Control Systems/Description and Operation/Fuel System Description)
Electrical Information Reference
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Circuit Testing (See: Accessories and Optional Equipment/Antitheft and Alarm Systems/Diagrams/Diagnostic Aids/General Electrical Diagnostic
Procedures/Circuit Testing/Circuit Testing)
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Connector Repairs (See: Accessories and Optional Equipment/Antitheft and Alarm Systems/Diagrams/Diagnostic Aids/General Electrical
Diagnostic Procedures/Connector Repairs/Connector Repairs)
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Testing for Intermittent Conditions and Poor Connections (See: Accessories and Optional Equipment/Antitheft and Alarm
Systems/Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit Testing/Testing For Intermittent and Poor Connections)
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Wiring Repairs (See: Accessories and Optional Equipment/Antitheft and Alarm Systems/Diagrams/Diagnostic Aids/General Electrical Diagnostic
Procedures/Wiring Repairs/Wiring Repairs)
Scan Tool Reference
Programming and Relearning (See: Testing and Inspection/Programming and Relearning) for scan tool information
Special Tools
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CH-48027 Digital Pressure Gage
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J 37287 Fuel Line Shut-off Adapter
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 relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
