For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Defogger Schematics
1 | Did you perform the Stationary Windows Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Stationary Windows
2 |

1. Start the engine.
2. Depress the rear window defogger switch.
3. Observe the rear window defogger indicator on the Heater and A/C Control Module.

Does the rear window defogger indicator illuminate?

Go to Step 3

Go to Step 10

3 | Connect a test lamp between 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 9
5 |

1. Turn OFF the ignition.
2. Remove the Heated Outside Rearview Mirror and Rear Window Defogger relay.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the battery positive voltage circuit of the Heated Outside Rearview Mirror and Rear Window Defogger relay switch and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 13

6 |

1. Connect a 40 amp fused jumper between the battery positive voltage circuit of the Heated Outside Rearview Mirror and Rear Window Defogger relay switch and the supply voltage circuit of the rear window defogger.
2. Connect a test lamp between the rear window defogger grid and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 7

7 |

1. Turn OFF the ignition.
2. Disconnect the harness connector of the Radio Antenna Amplifier.
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the supply voltage circuit of the rear window defogger and a good ground.

Does the test lamp illuminate?

Go to Step 8

Go to Step 14

8 | Test the supply voltage circuit of the rear window defogger between the Radio Antenna Amplifier and the rear window defogger grid 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 18 | Go to Step 12
9 | Test the ground circuit of the rear window defogger 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 18 | Go to Step 12
10 | Inspect for poor connections at the harness connector of the Heater and A/C 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 18 | Go to Step 15
11 | Inspect for poor connections at the Heated Outside Rearview Mirror and Rear Window Defogger 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 18 | Go to Step 16
12 | Inspect for poor connections at the harness connector of the Radio Antenna Amplifier. 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 18 | Go to Step 17
13 | Repair an open or high resistance in the battery positive voltage circuit of the Heated Outside Rearview Mirror and Rear Window Defogger relay switch. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 18 | --
14 | Repair an open or high resistance in the supply voltage circuit of the rear window defogger grid. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 18 | --
15 | Replace the Heater and A/C Control Module. Refer to Control Assembly Replacement in HVAC Systems - Automatic. Did you complete the replacement? | Go to Step 18 | --
16 | Replace the Heated Outside Rearview Mirror and Rear Window Defogger relay. Did you complete the replacement? | Go to Step 18 | --
17 | Replace the Radio Antenna Amplifier. Refer to Antenna Amplifier Replacement in Entertainment. Did you complete the replacement? | Go to Step 18 | --
18 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2