Hummer H2. Manual - part 1893

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Review the Exhaust System Description and Operation in order to familiarize yourself with the system 
functions. Refer to Exhaust System Description .  

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All diagnostics on a vehicle should follow a logical process. Strategy Based Diagnostics is a uniform 
approach for repairing all systems. The diagnostic flow is the place to start when repairs are necessary 
and may always be used in order to resolve a system problem. For a detailed explanation, refer to 
Strategy Based Diagnosis in General Information.  

Visual/Physical Inspection 

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Inspect for aftermarket or non-OEM devices such as, but not including; tailpipe extensions, headers, and 
exhaust cutouts. This could affect the operation and proper performance of the exhaust system.  

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Verify the exact operating conditions under which the concern exists. Note factors such as engine RPM, 
engine temperature, engine load, and frequency of concern.  

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Inspect the easily accessible or visible system components for obvious damage or conditions which could 
cause any symptom.  

Intermittent 

Test the vehicle under the same conditions that the customer reported in order to verify the system is operating 
as designed. 

Symptom List 

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom: 

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Loss of power 

Refer to Restricted Exhaust . 

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Poor acceleration 

Refer to Restricted Exhaust . 

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Poor fuel economy 

Refer to Restricted Exhaust . 

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Excessive smoke (diesel) 

Refer to Restricted Exhaust . 

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Exhaust hissing noise 

Refer to Exhaust Leakage . 

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Exhaust popping noise 

 

2004 Hummer H2 

2004 ENGINE Engine Exhaust - Hummer H2

  

Refer to Exhaust Leakage . 

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Exhaust rattle noise 

Refer to Exhaust Noise . 

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Loud exhaust noise 

Refer to Exhaust Noise . 

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Exhaust buzz, groan, hum noise 

Refer to Exhaust Noise . 

RESTRICTED EXHAUST 

Test Description 

The numbers below refer to the step numbers on the diagnostic table. 

3: The exhaust system has very low back pressure under normal conditions. If the exhaust system is 
restricted, a significant increase in the exhaust pressure is noticed on the J 35314-A Exhaust Back Presser 
Tester. Removing the heated oxygen sensor (HO2S) may set a DTC. When finishing this diagnostic table, 
be sure to clear all codes. See Special Tools and Equipment .  

4: This step will isolate the catalytic converter from the remainder of the exhaust system.  

7: Confirming that the condition has been fixed is essential. If the symptom still exists and the vehicle has 
a dual exhaust system, proceed to Step 2 and repeat diagnostic procedure on the opposite exhaust pipe.  

Restricted Exhaust 

CAUTION: While engine is operating, the exhaust system will become extremely hot. 

To prevent burns avoid contacting a hot exhaust system.

Step

Action

Value(s)

Yes

No

1

Did you verify the customers complaint?

-

Go to 

Step 2

-

2

Did you review the exhaust symptoms diagnostic 
information and perform the necessary inspections?

-

Go to 

Step 3

Go to 

Symptoms - 

Engine 

Exhaust

1. Remove the heated oxygen sensor (HO2S) that is in 

front of and closest to the catalytic converter. Refer 
to Heated Oxygen Sensor (HO2S) Replacement 
Bank 1 Sensor 1 or Heated Oxygen Sensor 
(HO2S) Replacement Bank 2 Sensor 1 in Engine 

20 kPa (3 psi)

 

2004 Hummer H2 

2004 ENGINE Engine Exhaust - Hummer H2

  

3

Controls - 6.0L (LQ4).  

2. Install the J 35314-A in place of the HO2S sensor. 

See Special Tools and Equipment .  

3. Start the engine.  

4. Increase and monitor the engine speed at 2,000 

RPM.  

5. Observe the exhaust system back pressure reading 

on the gauge.  

Does the reading exceed the specified value?

If equipped 

with a 4.8L, 

5.3L, or 6.0L - 

3.4 kPa (0.5 

psi)

Go to 

Step 4

Go to Step 7

4

1. Turn the engine off and place the ignition in the 

lock position.  

2. Remove the J 35314-A . See Special Tools and 

Equipment .  

3. Re-install the HO2S sensor. Refer to Heated 

Oxygen Sensor (HO2S) Replacement Bank 1 
Sensor 1 or Heated Oxygen Sensor (HO2S) 
Replacement Bank 2 Sensor 1 in Engine Controls 
- 6.0L (LQ4).  

4. Remove the post-catalyst HO2S sensor. Refer to 

Heated Oxygen Sensor (HO2S) Replacement 
Bank 1 Sensor 2 or Heated Oxygen Sensor 
(HO2S) Replacement Bank 2 Sensor 2 in Engine 
Controls - 6.0L (LQ4).  

5. Install the J 35314-A in place of the post HO2S 

sensor. See Special Tools and Equipment .  

6. Start the engine.  

7. Increase and monitor the engine speed at 2,000 

RPM.  

8. Observe the exhaust system back pressure reading 

on the gauge.  

Does the reading exceed the specified value?

20 kPa (3 psi)

If equipped 

with a 4.8L, 

5.3L, or 6.0L - 

3.4 kPa (0.5 

psi)

Go to 

Step 5

Go to Step 6

5

Inspect the exhaust system for the following conditions: 

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Damage in the exhaust pipe.  

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Debris in the exhaust pipe  

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Muffler internal failure.  

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Two-layer exhaust pipe separation.  

 
Did you find and correct the condition?

-

Go to 

Step 7

-

 

2004 Hummer H2 

2004 ENGINE Engine Exhaust - Hummer H2

  

EXHAUST LEAKAGE 

Exhaust Leakage 

6

Replace the catalytic converter. Refer to Catalytic 
Converter Replacement (Right Hand) . 
Did you find and correct the condition?

-

Go to 

Step 7

-

7

1. Remove the J 35314-A . See Special Tools and 

Equipment .  

2. Re-install the HO2S sensor. Refer to Heated 

Oxygen Sensor (HO2S) Replacement Bank 1 
Sensor 2 or Heated Oxygen Sensor (HO2S) 
Replacement Bank 2 Sensor 2 in Engine Controls 
- 6.0L (LQ4).  

3. Clear any codes.  

4. Road test the vehicle in order to verify the repair.  

Did you correct the condition?

-

System 

OK

Go to Step 2

Problem

Action

DEFINITION: An exhaust leak may show stains at the area of the leak. The leak may be felt by holding 
a hand close to the suspected areas or using a smoke pencil. The leak may make a popping or hissing 
noise.Refer to Symptoms - Engine Exhaust prior to beginning this table.

CAUTION:

While engine is operating, the exhaust system will become extremely hot. To prevent burns avoid 
contacting a hot exhaust system.

Misaligned or improperly installed 
exhaust system components.

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Align and tighten the components to the specifications. 
Refer to Fastener Tightening Specifications .  

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Ensure the exhaust hangers are in the proper locations 
and not loose.  

Exhaust leaks at the following 
connections: 

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Exhaust manifold to pipe  

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Flanges  

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Pipe clamps  

Tighten the components to the specifications. Refer to 
Fastener Tightening Specifications .

Seals or gaskets leaking. 

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Exhaust manifold to cylinder head  

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Exhaust pipes to exhaust manifold  

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Catalytic converter connection  

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EGR connections, if equipped  

Replace the leaking seal or gasket. Refer to the affected 
components procedure for service.

 

2004 Hummer H2 

2004 ENGINE Engine Exhaust - Hummer H2