For 1990-2009 cars
Master Electrical Component List
Defogger Schematics

### Circuit Description

The body control module (BCM) monitors the rear defogger switch input. When the rear defogger is turned ON (defog switch closed), the BCM grounds the coil side of the rear defog relay. This will energize the relay activating the rear defogger.

The first time in an ignition cycle that the rear defogger is activated, the rear defogger will remain ON for 15 minutes, or until the ignition switch is turned OFF. If the rear defogger is activated again during the same ignition cycle, the rear defogger will remain ON for 7 1/2 minutes, or until the ignition switch is turned OFF.

### Conditions for Running the DTC

The ignition is in RUN.

### Conditions for Setting the DTC

• | The BCM detects an open or short to ground in the rear defog relay control circuit when the relay is energized.

• | The condition exists for 30 seconds.

• | The BCM is not requesting the rear defogger system.

### Action Taken When the DTC Sets

• | The rear window defogger will be disabled until the condition is no longer present.

• | The LED on the defogger switch will not illuminate when pressed.

### Conditions for Clearing the DTC

• | This DTC will change from current to history when the fault is no longer present.

• | A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

### Test Description

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

1. Listen for an audible click when the REAR DEFOG relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

2. Verifies that the BCM is providing ground input to the REAR DEFOG relay.

3. Tests for a short to ground on the rear defog relay control circuit of the REAR DEFOG relay coil.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Defogger Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems
1 | Did you perform the Defogger Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Defogger
2 |

1. Turn the ignition ON, with the engine OFF.
2. With a scan tool, select from Special Functions the Rear Defogger Relay from the BCM output controls.
3. 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 Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3 |

1. Turn the ignition OFF.
2. Disconnect the REAR DEFOG relay.
3. Turn the ignition ON, with the engine OFF.
4. Connect a test lamp between the rear defog relay control circuit of the REAR DEFOG relay coil and B+.
5. With a scan tool, command the REAR DEFOG relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 4

Go to Step 5

4 |

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

Does the test lamp turn ON and OFF with each command?

Go to Step 7

Go to Step 9

5 | Test the rear defog relay control circuit of the REAR DEFOG relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 6
6 | Test the rear defog relay control circuit of the rear window defogger indicator for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8
7 | Inspect for poor connections 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 12 | Go to Step 10
8 | Inspect for poor connections at the harness connector of the 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 12 | Go to Step 11
9 | Repair an open or high resistance in the rear defog relay control circuit of the REAR DEFOG relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 12 | --
10 | Replace the REAR DEFOG relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | Go to Step 12 | --
11 | Important: Perform the programming or setup procedure for the replaced control module if required. Replace the BCM. Refer to Body Control Module Replacement in Body Control System for applicable replacement procedure. Did you complete the replacement? | Go to Step 12 | --
12 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK