Hummer H2. Manual - part 714

automatic day-night feature of the inside rearview mirror. Refer to Checking Aftermarket Accessories
in Wiring Systems.  

z

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

Intermittent 

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for 
Intermittent Conditions and Poor Connections in Wiring Systems. 

Symptom List 

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

z

Defogger Inoperative - Rear Window  

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Defogger Grid Lines Diagnosis  

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Mirrors - Automatic Day-Night Inoperative  

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Mirrors - Temperature Displays SC or OC  

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Mirrors - Compass Display Inoperative or Inaccurate  

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Mirrors - Temperature Display Inaccurate  

DEFOGGER INOPERATIVE - REAR WINDOW 

Defogger Inoperative - Rear Window 

Step

Action

Yes

No

Schematic Reference:Defogger Schematics 
Connector End View Reference:Stationary Windows Connector End Views

1

Did you perform the Defogger Diagnostic System 
Check?

Go to Step 2

Go to Diagnostic 

System Check - 

Defogger

2

1. Start the engine.  

2. Depress the rear window defogger switch.  

3. Observe the rear window defogger indicator 

on the HVAC Control Module.  

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 8

3

Connect a test lamp between the left side of the rear 
window defogger grid and a good ground. 
Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4

Connect a test lamp between the left side of the rear 
window defogger grid and the right side of the rear 
window defogger grid. 
Does the test lamp illuminate?

Go to Testing for 

Intermittent Conditions 

and Poor Connections in 

Wiring Systems

Go to Step 10

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Stationary Windows - Hummer H2

  

5

1. Turn OFF the ignition.  

2. Disconnect the DEFOG relay.  

3. Turn ON the ignition, with the engine OFF.  

4. Connect a test lamp between the battery 

positive voltage circuit of the DEFOG relay 
switched input and a good ground.  

Does the test lamp illuminate?

Go to Step 6

Go to Step 7

6

1. Connect a 40 amp fused jumper between the 

battery voltage circuit of the DEFOG relay 
switched input and the relay switched output 
to the supply voltage circuit of the rear 
window defogger.  

2. Connect a test lamp between the left side of 

the rear window defogger grid and a good 
ground.  

Does the test lamp illuminate?

Go to Step 9

Go to Step 12

7

Test the battery positive voltage circuit of the 
DEFOG relay switched input for an open or high 
resistance. Refer to Circuit Testing and Wiring 
Repairs in Wiring Systems. 
Did you find and correct the condition?

Go to Step 15

Go to Step 11

8

Inspect for poor connection at the harness connector 
of the HVAC Control Module. Refer to Testing for 
Intermittent Conditions and Poor Connections 
and Connector Repairs in Wiring Systems. 
Did you find and correct the condition?

Go to Step 15

Go to Step 13

9

Inspect for poor connection at the DEFOG relay. 
Refer to Testing for Intermittent Conditions and 
Poor Connections and Connector Repairs in 
Wiring Systems. 
Did you find and correct the condition?

Go to Step 15

Go to Step 14

10

Repair an open or high resistance in the ground 
circuit of the rear window defogger. Refer to 
Wiring Repairs in Wiring Systems. 
Did you complete the repair?

Go to Step 15

-

11

Repair a short to ground in the supply voltage circuit 
of the rear window defogger. Refer to Wiring 
Repairs in Wiring Systems. 
Did you complete the repair?

Go to Step 15

-

12

Repair an open or high resistance in the supply 
circuit of the rear window defogger. Refer to 
Wiring Repairs in Wiring Systems. 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Stationary Windows - Hummer H2

  

DEFOGGER GRID LINES DIAGNOSIS 

This test is for reference only. A grid line fault requires the rear window replacement. Refer to Rear Lift 
Window Replacement . 

1. Start the engine.  

2. Activate the rear window defogger system.  

3. Connect a test lamp to a good ground. 

Did you complete the repair?

Go to Step 15

-

13

Replace the HVAC Control Module. Refer to 
HVAC Control Module Replacement in HVAC 
Systems - Automatic. 
Did you complete the replacement?

Go to Step 15

-

14

Replace the DEFOG relay. 
Did you complete the replacement?

Go to Step 15

-

15

Operate the system in order to verify the repair. 
Did you correct the condition?

System OK

Go to Step 2

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Stationary Windows - Hummer H2

  

Fig. 4: Defogger Grid Line Zones 
Courtesy of GENERAL MOTORS CORP. 

4. Move the test lamp probe from zone 5 to zone 1 along each grid line. 

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If the test lamp shows full brilliance at both ends of the grid lines. Inspect for an open or poor 
connection in the ground circuit of the rear window defogger grid. Refer to Testing for 
Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. 

IMPORTANT: The test lamp brilliance will decrease proportionately to the increased 

resistance in the grid line as the probe is moved from the battery positive 
bus wire to the ground bus wire. The test lamp brilliance may vary from 
one window to another.

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Stationary Windows - Hummer H2