GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Malibu 🢒 Body 🢒 Stationary Windows 🢒 Rear Window Defogger Inoperative

Diagnostic Aids

The vehicle is equipped with one of two different types of heating, ventilation and air conditioning (HVAC) systems which affect rear window defog operation. These are:

    • Manual air temperature control (RPO C60)
    • Automatic air temperature control (RPO C68)

Specific circuit and component failures may result in different symptoms depending upon which type of HVAC system the vehicle uses. Carefully follow the Test Descriptions, as well as the instructions contained in each table step in order to avoid misdiagnosis.

Test Description

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

  1. The rear window defog feature is operated by activating the rear defog switch, which is an integral part of the HVAC control module. This step begins to determine if the ground circuit to the HVAC control module, which affects defog switch operation, has failed. If this ground has failed, both the AC and the rear window defog systems and indicators may still operate when the headlamps are turned OFF, but not when the headlamps are ON. Turning On the headlamps verifys that the test results are accurate.

    2.

  2. Listen for an audible click to help determine if the rear defog relay operates.

    3.

  3. Listen for an audible click to help determine if the rear defog relay operates.

    4.

  4. On vehicles equipped with RPO C60, this step will determine if the failure is in the defog switch signal circuit. However, vehicles equipped with RPO C68 do not include this circuit. Therefore, on vehicles with C68, you must answer No to the question or omit this step and proceed directly to the next step.

    5.

  5. On vehicles equipped with RPO C60, this step will determine if the failure is in the defog indicator supply voltage circuit. However, vehicles equipped with RPO C68 do not include this circuit. Therefore, on vehicles with C68, you must answer No to the question and proceed to replacement of the HVAC control module.

Step

Action

Yes

No

Schematic Reference: Defogger Schematics

Connector End View Reference: Stationary Windows Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: Make sure that system voltage is near normal operating range on the vehicle. This will affect the illumination of the rear window defogger indicator.

    • Turn OFF, then turn ON the ignition, with the engine OFF.
    • Depress the rear window defog switch button.

Does the rear window defog system operate properly?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Does only the rear window defog indicator on the HVAC control module fail to operate?

Go to Step 15

Go to Step 4

4

Does only the rear window defog grid fail to operate?

Go to Step 7

Go to Step 5

5

  1. Turn ON the headlamps.
  2. Attempt to operate the air conditioning system with the A/C switch on the HVAC control module.
  3. Observe the air conditioning indicator.

Does the A/C system indicator fail to operate?

Go to Step 16

Go to Step 6

6

Is the vehicle equipped with RPO C68?

Go to Step 18

Go to Step 14

7
  1. Turn OFF the ignition.
  2. Disconnect the rear window defog relay .
  3. Turn ON the ignition, with the engine OFF.
  4. With a test lamp connected to a good ground, probe the switched battery voltage input circuit of the relay socket.

Does the test lamp illuminate?

Go to Step 8

Go to Step 22

8
  1. With a test lamp connected to a good ground, probe the rear defog relay control circuit of the relay socket.
  2. Depress the rear window defog switch button until the rear window defog indicator illuminates.

Does the test lamp illuminate?

Go to Step 9

Go to Step 12

9
  1. Connect the test lamp between the rear defog relay control circuit and the rear defog relay ground circuit of the relay socket.
  2. Depress the rear window defogger switch button until the rear window defog indicator illuminates.

Does the test lamp illuminate?

Go to Step 10

Go to Step 20

10

  1. Connect the rear defog relay.
  2. Disconnect the rear defog element supply voltage circuit connector from the rear window defog grid.
  3. With a test lamp connected to a good ground, probe the rear defog element supply voltage circuit of the connector.
  4. Depress the rear window defog switch button until the rear window defog indicator illuminates.

Does the test lamp illuminate?

Go to Step 11

Go to Step 13

11

  1. Disconnect the ground circuit connector from the rear window defog grid.
  2. Connect the test lamp between the rear defog element supply voltage circuit and the ground circuit.
  3. Depress the rear window defog switch button until the rear window defog indicator illuminates.

Does the test lamp illuminate?

Go to Defogger Grid Lines Diagnosis

Go to Step 21

12

Test the rear defog relay control circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 19

13

Test the rear defog element supply voltage circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 17

14

Test the rear defog switch signal circuit for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 18

15

Important: If the vehicle is equipped with RPO C68, proceed to replacement of the HVAC control module.

Test the rear defog indicator supply voltage circuit for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 18

16

Test the ground circuit of the HVAC control module for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 26

Go to Step 18

17

Inspect for a poor connection at the rear 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 26

Go to Step 24

18

Inspect for a 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 26

Go to Step 23

19

Inspect for a poor connection at the harness connector of the body control module (BCM). 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 26

Go to Step 25

20

Repair an open or high resistance in the ground circuit of the rear window defog relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

21

Repair an open in the ground circuit of the rear window defog grid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

22

Repair an open or short to ground in the switched battery voltage input circuit of the relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 26

--

23

Replace the HVAC control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 26

--

24

Replace the rear defog relay.

Did you complete the replacement?

Go to Step 26

--

25

Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 26

--

26

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2