For 1990-2009 cars

### Test Description

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

1. If the Rear Defog Load Shed data parameters are displayed as Active, system voltage may be low due to a number of loads enabled on the vehicle, while the ignition is ON. This may be normal due to the number of loads enabled or the vehicle may have a charging system or battery concern.

2. Gain access to the REAR DEFOG relay located in the right rear fuse block and listen for an audible click when the relay operates. Command both the ON and OFF states of the REAR DEFOG relay. Repeat the commands as necessary.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Defogger Schematics Connector End View Reference: Window Systems Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn ON the ignition, with the engine OFF.
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 5

3 |

1. Connect a test lamp between the rear window defogger grid at the right side and ground.
2. Turn ON the rear defogger switch and wait 5 seconds.

Does the test lamp illuminate?

Go to Step 4

Go to Step 7

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 | Go to Step 17
5 | With a scan tool, observe the Rear Defog Status data parameter in the rear integration module (RIM) outputs list. Does the scan tool display ON? | Go to Step 6 | Go to Step 14
6 | With a scan tool, observe the Rear Defog Load Shed 1, 2, and 3 data parameters in the RIM data list. Does the scan tool display Active? | Go to Diagnostic System Check - Vehicle | Go to Step 14
7 |

1. Install a scan tool.
2. With a scan tool, command the REAR DEFOG relay ON and OFF.

Do you hear a click when you command the REAR DEFOG relay ON and OFF?

Go to Step 10

Go to Step 8

8 |

1. Turn OFF the ignition.
2. Disconnect the REAR DEFOG relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the ignition voltage circuit of the REAR DEFOG relay coil and ground.

Does the test lamp illuminate?

Go to Step 9

Go to Step 18

9 |

1. Connect a DMM between the rear defog relay control circuit and the ignition voltage circuit of the REAR DEFOG relay coil.
2. With a scan tool, command the REAR DEFOG relay ON.

Does the scan tool display battery voltage for approximately 5 seconds and then return to 0 volts?

Go to Step 15

Go to Step 12

10 |

1. Turn OFF the ignition.
2. Disconnect the REAR DEFOG relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the battery positive voltage circuit of the REAR DEFOG relay switched input and ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 13

11 | Test the rear window defogger voltage supply circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 23 | Go to Step 15
12 | Test the REAR DEFOG relay control circuit for an open, high resistance, or short to battery voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 23 | Go to Step 16
13 | Test the battery positive voltage circuit of the REAR DEFOG relay switched input for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 23 | Go to Step 19
14 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 23 | Go to Step 20
15 | Inspect for poor connections at the REAR DEFOG relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 23 | Go to Step 21
16 | Inspect for poor connections at the harness connector of the RIM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | Go to Step 23 | Go to Step 22
17 | Locate and repair an open or high resistance in the ground circuit of the rear window defogger. Refer to Wiring Repairs. Did you complete the repair? | Go to Step 23 | --
18 | Locate and repair an open or a high resistance in the ignition voltage circuit of the REAR DEFOG relay coil. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 23 | --
19 | Locate and repair a short to ground in the supply voltage circuit of the rear window defogger. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 23 | --
20 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 23 | --
21 | Replace the REAR DEFOG relay. Refer to Relay Replacement. Did you complete the replacement? | Go to Step 23 | --
22 | Replace the RIM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 23 | --
23 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2