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

z

Defogger Grid Lines Diagnosis

z

Mirrors - Automatic Day-Night Inoperative

z

Mirrors - Temperature Displays SC or OC

z

Mirrors - Compass Display Inoperative or Inaccurate

z

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.

z

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