Hummer H2. Manual - part 1696

BASE ENGINE MISFIRE WITH ABNORMAL INTERNAL LOWER ENGINE NOISES 

Base Engine Misfire with Abnormal Internal Lower Engine Noises 

Engine Cooling in Engine Cooling. 
Coolant consumption may or may not cause the engine to 
overheat.

6.0L.  

z

Inspect the cylinder heads, engine 
block, and/or head gaskets. Refer to 
Coolant in Combustion Chamber . 

z

Repair or replace as required.  

Worn piston rings 
Oil consumption may or may not cause the engine to 
misfire.

z

Inspect the spark plugs for oil 
deposits. Refer to Spark Plug 
Inspection in Engine Controls - 
6.0L.  

z

Inspect the cylinders for a loss of 
compression. Refer to Engine 
Compression Test .  

z

Perform cylinder leak down and 
compression testing to identify the 
cause. Refer to Cylinder Leakage 
Test .  

z

Repair or replace as required.  

A damaged crankshaft reluctor wheel 
A damaged crankshaft reluctor wheel can result in different 
symptoms depending on the severity and location of the 
damage. 

z

Systems with electronic communications, DIS or coil 
per cylinder, and severe reluctor ring damage may 
exhibit periodic loss of crankshaft position, stop 
delivering a signal, and then sync the crankshaft 
position.  

z

Systems with electronic communication, DIS or coil 
per cylinder, and slight reluctor ring damage may 
exhibit no loss of crankshaft position and no misfire 
may occur. However, a P0300 DTC may be set.  

z

Systems with mechanical communications, high 
voltage switch, and severe reluctor ring damage may 
cause additional pulses and effect fuel and spark 
delivery to the point of generating a P0300 DTC or 
P0336.  

Replace the sensor and/or crankshaft as 
required.

Cause

Correction

Abnormalities, such as severe cracking, bumps or missing 
areas in the accessory drive belt 
Abnormalities in the accessory drive system and/or 

Replace the drive belt. Refer to Drive 
Belt Replacement - Accessory .

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

BASE ENGINE MISFIRE WITH ABNORMAL VALVE TRAIN NOISE 

Base Engine Misfire with Abnormal Valve Train Noise 

components may cause engine RPM variations, noises similar 
to a faulty lower engine and also lead to a misfire condition. A 
misfire code may be present without an actual misfire 
condition.
Worn, damaged, or mis-aligned accessory drive components or 
excessive pulley runout 
A misfire code may be present without an actual misfire 
condition.

Inspect the components, repair or 
replace as required.

Loose or improperly installed engine flywheel or crankshaft 
balancer 
A misfire code may be present without an actual misfire 
condition.

Repair or replace the flywheel and/or 
balancer as required. 
Refer to Engine Flywheel Replacement
or Crankshaft Balancer Replacement .

Worn piston rings 
Oil consumption may or may not cause the engine to misfire.

z

Inspect the spark plugs for oil 
deposits. Refer to Spark Plug 
Inspection in Engine Controls - 
6.0L.  

z

Inspect the cylinders for a loss of 
compression. Refer to Engine 
Compression Test .  

z

Perform cylinder leak down and 
compression testing to determine 
the cause. Refer to Cylinder 
Leakage Test .  

z

Repair or replace as required.  

Worn crankshaft thrust bearings 
Severely worn thrust surfaces on the crankshaft and/or thrust 
bearing may permit fore and aft movement of the crankshaft 
and create a DTC without an actual misfire condition.

Replace the crankshaft and bearings as 
required.

Cause

Correction

Worn or loose rocker arms 
The rocker arm bearing end caps and/or 
needle bearings should be intact within the 
rocker arm assembly.

Replace the valve rocker arms as required.

Worn or bent pushrods

z

Replace the pushrods.  

z

Inspect the top of the pistons for valve contact. If 
the top of the piston shows valve contact, replace 
the piston and pin assembly.  

Stuck valves 
Carbon buildup on the valve stem can cause 
the valve not to close properly.

Repair or replace as required.

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

BASE ENGINE MISFIRE WITH COOLANT CONSUMPTION 

Base Engine Misfire with Coolant Consumption 

BASE ENGINE MISFIRE WITH EXCESSIVE OIL CONSUMPTION 

Base Engine Misfire with Excessive Oil Consumption 

ENGINE NOISE ON START-UP, BUT ONLY LASTING A FEW SECONDS 

Engine Noise on Start-Up, but Only Lasting a Few Seconds 

Excessively worn or mis-aligned timing 
chain

Replace the timing chain and sprockets as required.

Worn camshaft lobes

Replace the camshaft and valve lifters.

Sticking lifters

Replace as required.

Cause

Correction

Faulty cylinder head gaskets and/or cracking or other 
damage to the cylinder heads and engine block 
cooling system passages - Refer to Diagnostic 
Starting Point - Engine Cooling in Engine Cooling.
Coolant consumption may or may not cause the 
engine to overheat.

z

Inspect for spark plugs saturated by 
coolant. Refer to Spark Plug Inspection in 
Engine Controls - 6.0L.  

z

Perform a cylinder leak down test. Refer to 
Cylinder Leakage Test .  

z

Inspect the cylinder heads and engine block 
for damage to the coolant passages and/or a 
faulty head gasket. Refer to Coolant in 
Combustion Chamber .  

z

Repair or replace as required.  

Cause

Correction

Worn valves, valve guides and/or 
valve stem oil seals

z

Inspect the spark plugs for oil deposits. Refer to Spark Plug 
Inspection in Engine Controls - 6.0L.  

z

Repair or replace as required.  

Worn piston rings 
Oil consumption may or may not 
cause the engine to misfire.

z

Inspect the spark plugs for oil deposits. Refer to Spark Plug 
Inspection in Engine Controls - 6.0L.  

z

Inspect the cylinders for a loss of compression. Refer to 
Engine Compression Test .  

z

Perform cylinder leak down and compression testing to 
determine the cause. Refer to Cylinder Leakage Test .  

z

Repair or replace as required.  

Cause

Correction

Incorrect oil filter without anti-drainback 
feature

Install the correct oil filter.

Incorrect oil viscosity

1. Drain the oil.  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

UPPER ENGINE NOISE, REGARDLESS OF ENGINE SPEED 

Upper Engine Noise, Regardless of Engine Speed 

2. Install the correct viscosity oil.  

High valve lifter leak down rate

Replace the lifters as required.

Worn crankshaft thrust bearing

1. Check the crankshaft end play.  

2. Inspect the thrust bearing and crankshaft.  

3. Repair or replace as required.  

Damaged or faulty oil filter by-pass valve

z

Inspect the oil filter by-pass valve for proper 
operation.  

z

Repair or replace as required.  

Cause

Correction

Low oil pressure

z

Perform an oil pressure test. Refer to Oil Pressure 
Diagnosis and Testing .  

z

Repair or replace as required.  

Loose and/or worn valve rocker arm 
attachments

z

Inspect the valve rocker arm, bolt, and pedestal.  

z

Repair or replace as required.  

Worn or damaged valve rocker arm

z

Inspect the rocker arm for wear or missing needle bearings 

z

Replace the valve rocker arms as required.  

Bent or damaged push rod

Inspect the following components and replace as required: 

z

The valve rocker arm  

z

The valve push rod  

z

The valve lifter  

z

The valve lifter guide  

z

The piston  

 
Inspect the top of the pistons for valve contact. If the top of the 
piston shows valve contact, replace the piston and pin assembly.

Improper lubrication to the valve 
rocker arms

Inspect the following components and repair or replace as 
required: 

z

The valve rocker arm  

z

The valve push rod  

z

The valve lifter  

z

The oil filter bypass valve  

z

The oil pump and pump screen  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2