Hummer H2. Manual - part 1592

Engine 
Mechanical

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Inspect engine mechanical for the following: 

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Compression-Refer to Engine Compression Test in Engine Mechanical.  

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Sticking or leaking valves  

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Worn camshaft lobes  

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Valve timing  

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Bent push rods  

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Worn rocker arms  

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Broken valve springs  

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Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil 
Consumption Diagnosis in Engine Mechanical.  

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For incorrect basic engine parts inspect for the following: 

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The camshaft - Refer to Camshaft and Bearings Cleaning and 
Inspection in Engine Mechanical.  

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The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in 
Engine Mechanical.  

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The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings 
Cleaning and Inspection in Engine Mechanical.  

Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnostic 
procedures.

Additional 
Inspections

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Visually and physically check the vacuum hoses for splits, kinks, and proper 
connections and routing as shown on Vehicle Emission Control Information 
label.  

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Inspect the transmission torque converter clutch (TCC) operation. The scan tool 
should indicate a RPM drop, when the system commands the TCC ON. Refer to 
Diagnostic System Check - Automatic Transmission in Automatic 
Transmission - 4L60-E.  

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Inspect the exhaust system for a possible restriction. Inspect for the following: 

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Inspect the exhaust system for damaged or collapsed pipes.  

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Inspect the mufflers for heat distress or possible internal failure.  

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Inspect for possible plugged catalytic converters. Refer to Restricted 
Exhaust in Engine Exhaust.  

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Electromagnetic interference (EMI) on the reference circuit can cause an engine 
miss condition. A scan tool can usually detect EMI by monitoring the engine 
RPM. A sudden increase in RPM with little change in actual engine RPM change 
indicates EMI is present. Inspect for high voltage components, near ignition 
control circuits, if a condition exists.  

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Inspect the park neutral position (PNP) switch circuit. Refer to Park/Neutral 
Position Switch Adjustment in Automatic Transmission - 4L60-E.  

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Inspect the intake and the exhaust manifold passages for casting flash.  

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

POOR FUEL FILL QUALITY 

Poor Fuel Fill Quality 

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Inspect the brake system for dragging or improper operation. Refer to Brakes 
Drag in Hydraulic Brakes. Verify that the vehicle operator does not drive with a 
foot on the brake pedal.  

Problem

Causes

DEFINITION: Difficulty when refueling the vehicle.
Difficult to fill

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The check valve is stuck closed.  

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The fill limiter vent valve is stuck closed.  

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The evaporative emission (EVAP) canister is restricted.  

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The EVAP canister vent solenoid is stuck closed.  

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Restricted EVAP pipes  

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High Reid vapor pressure  

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High fuel temperature  

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The fuel filler hose/pipe is pinched, kinked or blocked.  

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The fuel feed hose, or crossover hose, is pinched, kinked 
or blocked.  

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The ignition switch is ON.  

Over fill

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The pressure relief valve in the fill limiter vent valve is 
stuck open.  

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The pressure relief valve in the fill limiter vent is valve 
leaking.  

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The fill limiter vent valve is stuck open.  

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The fill limiter vent valve is leaking.  

Premature shut-off of the fuel 
dispensing nozzle

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The check valve is stuck closed.  

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The fill limiter vent valve is stuck closed.  

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The EVAP canister is restricted.  

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The EVAP canister vent solenoid is stuck closed.  

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Restricted EVAP pipes  

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High Reid vapor pressure  

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High fuel temperature  

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The fuel filler hose/pipe is pinched, kinked or blocked.  

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The fuel feed hose, or crossover hose, is pinched, kinked 
or blocked.  

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The ignition switch is ON.  

Fuel spit back

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The check valve is stuck open.  

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

ROUGH, UNSTABLE, OR INCORRECT IDLE AND STALLING 

Rough, Unstable, or Incorrect Idle and Stalling 

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The check valve is stuck closed.  

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The check valve is leaking.  

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High Reid vapor pressure  

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High fuel temperature  

Liquid fuel in the EVAP canister

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The fill limiter vent valve is stuck open.  

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The fill limiter vent valve is leaking.  

Liquid fuel leak

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The pressure relief valve in the fill limiter vent valve is 
stuck open.  

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The pressure relief valve in the fill limiter vent valve is 
leaking.  

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The fuel filler hose is loose or torn.  

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The fuel feed hose, or crossover hose, is loose or torn.  

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The fill limiter vent valve is stuck open.  

Fuel odor

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The pressure relief valve in the fill limiter vent valve is 
stuck open.  

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The pressure relief valve in the fill limiter vent valve is 
leaking.  

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The EVAP canister is saturated.  

Inspections

Action

DEFINITION: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle 
speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary 
Inspections

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Refer to Important Preliminary Inspections Before Starting in Symptoms - 
Engine Controls .  

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Search for bulletins.  

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Verify that the powertrain control module (PCM) grounds are clean, tight, and in 
the proper locations. Refer to Power and Grounding Component Views in 
Wiring Systems and Engine Controls Schematics .  

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Remove and inspect the air filter element for dirt or for restrictions. Refer to Air 
Cleaner Element Replacement . Replace as necessary.  

Fuel System

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Inspect the fuel injectors. Refer to Fuel Injector Coil Test , Fuel Injector 
Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .  

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Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis .  

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Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-
Fuel Diagnosis (without Special Tool and E85) or Alcohol/Contaminants-in-
Fuel Diagnosis (with Special Tool) .  

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Inspect that each fuel injector harness is connected to the correct 

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

injector/cylinder. Relocate fuel injector harnesses as necessary.  

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Inspect for the following that may cause the engine to run rich: 

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Water intrusion in the heated oxygen sensor (HO2S) connector  

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Engine oil contaminated by fuel  

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An evaporative emissions (EVAP) canister purge condition  

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Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

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Leaking fuel injectors - Refer to Fuel System Diagnosis .  

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An inaccurate mass air flow (MAF) sensor  

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Blockage on the inlet screen of the MAF sensor - Refer to Mass Air Flow 
(MAF)/Intake Air Temperature (IAT) Sensor Replacement .  

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Vacuum hoses that are split, kinked, or improperly connected  

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An air intake duct that is collapsed or restricted-Refer to Air Cleaner 
Resonator Outlet Duct Replacement .  

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An air filter that is dirty or restricted - Refer to Air Cleaner Element 
Replacement .  

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Inspect for the following conditions that may cause the engine to run lean: 

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Water intrusion in the HO2S connector  

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An exhaust leak between the HO2S and the engine-Refer to Exhaust 
Leakage in Engine Exhaust.  

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Vacuum leaks  

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Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

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Restricted fuel injectors - Refer to Fuel Injector Balance Test with 
Special Tool or Fuel Injector Balance Test with Tech 2 .  

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An inaccurate MAF sensor  

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Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis 
(without Special Tool and E85) or Alcohol/Contaminants-in-Fuel 
Diagnosis (with Special Tool) .  

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Vacuum hoses that are split, kinked, or improperly connected  

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

Sensor/System

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Inspect the crankcase ventilation valve for proper operation. Refer to Crankcase 
Ventilation System Inspection/Diagnosis in Engine Mechanical.  

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Use a scan tool in order to monitor the knock sensor (KS) system for excessive 

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2