For 1990-2009 cars

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Defogger Schematics
1 | Did you review the Rear Window Defogger Description and Operation and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Stationary Windows
2 |

1. Start the engine.
2. Depress the defogger switch ON.

Does the defogger grid warm?

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

Go to Step 3

3 | If the defogger indicator illuminates the fault is between S257 and G401. Does the defogger indicator illuminate? | Go to Step 4 | Go to Step 7
4 |

1. Start the engine.
2. Depress the defogger switch ON.
3. Connect a test lamp between the defogger connectors.

Does the test lamp illuminate?

Go to Grid Line Repair or Bus Bar Lead Terminal Repair

Go to Step 5

5 | Test the defogger grid ground circuit for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 6
6 | Test the defogger grid supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | --
7 |

1. Disconnect the defogger switch. Refer to Rear Window Defogger Switch Replacement for access.
2. Inspect the defogger indicator bulb.
3. Depress the defogger switch.
4. Test for a high resistance or for an open through the closed switch contacts.

Does the switch test OK?

Go to Step 8

Go to Step 13

8 | Test the defogger switch ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 9
9 | Test the defogger switch signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 10
10 | Test the defogger switch indicator supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 11
11 | Test the defogger relay supply voltage circuits for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 12
12 | Test the defogger relay ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 17 | Go to Step 14
13 | Inspect for a poor connection at the harness connector of the defogger switch. 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 17 | Go to Step 15
14 | Inspect for a poor connection at the harness connector of the 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 17 | Go to Step 16
15 | Replace the defogger switch. Refer to Rear Window Defogger Switch Replacement . Did you find and correct the condition? | Go to Step 17 | --
16 | Replace the defogger relay. Refer to Rear Window Defogger Relay Replacement . Did you find and correct the condition? | Go to Step 17 | --
17 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3