Hummer H2. Manual - part 1549

System Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the
camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring
variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events.
A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain
driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC
overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated
standards, DTC P0300 will set.

Conditions for Running the DTC

DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0220, P0315,
P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1120, P1258 are not set.

The engine speed is between 450-5,000 RPM.

The ignition voltage is between 10-18 volts.

The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).

The fuel level is more than 10 percent.

The throttle angle is steady within 1 percent.

The anti-lock brake system (ABS) and the traction control system are not active.

The transmission is not changing gears.

The A/C clutch is not changing states.

The PCM is not in fuel shut-off or decel fuel cut-off mode.

The PCM is not receiving a rough road signal.

Conditions for Setting the DTC

The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission
levels to exceed mandated standards.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition
cycle that the diagnostic runs and fails.

The control module records the operating conditions at the time the diagnostic fails. The first time the
diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic
reports a failure on the second consecutive ignition cycle, the control module records the operating
conditions at the time of the failure. The control module writes the operating conditions to the Freeze
Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles
that the diagnostic runs and does not fail.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other
emission related diagnostic.

Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are
possible sources of vibration:

{

Thickness variation of the brake rotors-Refer to Symptoms - Hydraulic Brakes in Hydraulic
Brakes.

{

The drive shaft not balanced-Refer to Vibration Analysis - Driveline in Vibration Diagnosis and
Correction.

{

Worn or damaged accessory drive belt-Refer to Symptoms - Engine Mechanical in Engine
Mechanical - 4.8L, 5.3L and 6.0L

There may be more or less cylinders actually misfiring than indicated by the scan tool.

Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or
misfiring.

If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and
ground circuits for that bank. Refer to Engine Controls Schematics .

Test Description

The number below refers to the step number on the diagnostic table.

2: If the actual CKP variation values are not within the learned values, the misfire counters may
increment.

DTC P0300

Step

Action

Values

Yes

Did you perform the Diagnostic System Check-
Engine Controls?

Go to Step 2

Go to Diagnostic

System Check -

Engine Controls

1. Start the engine.

2. Allow the engine to idle or operate within

the conditions listed in the Freeze
Frame/Failure Records.

IMPORTANT:

You must perform the crankshaft position
(CKP) system variation learn procedure
before proceeding with this diagnostic table.
Refer to CKP System Variation Learn
Procedure .

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

3. Monitor all of the Misfire counters with

the scan tool.

Are any of the Misfire current counters
incrementing?

Go to Step 3

Go to Diagnostic

Aids

Are any other DTCs set?

Go to Diagnostic

Trouble Code

(DTC) List

Go to Step 4

Can any abnormal engine noise be heard?

Go to Symptoms -

Engine Mechanical

in Engine

Mechanical - 4.8L,

5.3L and 6.0L

Go to Step 5

Does the scan tool indicate that the heated
oxygen sensor (HO2S) bank 1 sensor 1 or HO2S
bank 2 sensor 1 voltage parameters are below
the specified value?

200
mV

Go to DTC P0131

or P0151

Go to Step 6

Does the scan tool indicate that the HO2S bank
1 sensor 1 or HO2S bank 2 sensor 1 voltage
parameters are fixed above the specified value?

900
mV

Go to DTC P0132

or P0152

Go to Step 7

Inspect the following components:

The vacuum hoses and seals for splits,
restrictions, and improper connections -
Refer to Emission Hose Routing
Diagram .

The throttle body and intake manifold for
vacuum leaks

The crankcase ventilation system for
vacuum leaks - Refer to Crankcase
Ventilation System
Inspection/Diagnosis in Engine
Mechanical - 4.8L, 5.3L and 6.0L.

The powertrain control module (PCM)
grounds for corrosion and loose
connections - Refer to Ground
Distribution Schematics in Wiring
Systems.

The exhaust system for restrictions - Refer
to Restricted Exhaust in Engine Exhaust.

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

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

Did you find and correct the condition?

Go to Step 20

Go to Step 8

1. Turn OFF the ignition.

2. Disconnect the spark plug wire from the

spark plug that corresponds to the Misfire
Current counters that were incrementing.
Refer to Spark Plug Wire Replacement .

3. Install the J 26792 Spark Tester.

4. Start the engine.

Does the spark jump the tester gap?

IMPORTANT:

An erratic or inconsistent spark is
considered a no spark.

Go to Step 10

Go to Step 9

1. Remove the spark plug wire for the

affected cylinders. Refer to Spark Plug
Wire Replacement .

2. Inspect the spark plug wire. Refer to

Spark Plug Wire Inspection .

3. Measure the resistance of the spark plug

wire with a DMM.

Is the spark plug wire resistance less than the
specified value?

700

ohm

Go to Electronic

Ignition (EI)

System Diagnosis

Go to Step 19

1. Remove the spark plug from the cylinder

that indicated a misfire. Refer to Spark
Plug Replacement .

2. Inspect the spark plug. Refer to Spark

Plug Inspection .

Does the spark plug appear to be OK?

Go to Step 11

Go to Step 12

1. Exchange the suspected spark plug with

another cylinder that is operating
properly. Refer to Spark Plug
Replacement .

2. Operate the vehicle under the same

conditions that the misfire occurred.

Did the misfire move with the spark plug?

Go to Step 18

Go to Step 15

Is the spark plug oil or coolant fouled?

Go to Symptoms -

Engine Mechanical

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls Diagnosis (DTC P0171/P0174 To DTC P0507 (TAC)) - 4.8L, 5.3L, and

6.0L - Hummer H2

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