Circuit Description
The body control module (BCM) monitors the rear defogger switch input. When the rear defogger is turned ON, the rear defog switch is closed and the BCM supplies the battery positive voltage to the coil side of the rear defog relay. This will energize the relay activating the rear defogger.
The first time that the rear defogger is activated in an ignition cycle, the rear defogger will remain ON for 10 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 5 minutes, or until the ignition switch is turned OFF.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B0285 Electronic Rear Defrost Circuit Low |
| • | DTC B0286 Electronic Rear Defrost Circuit High |
Conditions for Running the DTC
The ignition is in RUN.
Conditions for Setting the DTC
| • | The BCM detects an open, short to ground, or short to voltage in the rear defog relay control circuit. |
| • | 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 inoperative if the circuit is open or shorted to ground. |
| • | The rear window defogger will be ON if the circuit is shorted to voltage. |
| • | The rear defogger indicator may not illuminate when the rear defogger switch is activated or may always be illuminated. |
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.
-
Listen for an audible click when the rear defog relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
-
This step verifies that the BCM is providing battery positive voltage input to the rear defog relay.
-
This step tests for a short to ground, or short to voltage 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 | |||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |||||||||
Do you hear a click when you command the Rear Defogger Relay ON and OFF? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | |||||||||
Does the test lamp turn ON and OFF with each command? | Go to Step 4 | Go to Step 5 | |||||||||
4 |
Does the test lamp turn ON and OFF with each command? | Go to Step 6 | Go to Step 8 | ||||||||
Test the rear defog relay control circuit and rear defog indicator control circuit for the following:
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 11 | Go to Step 7 | |||||||||
6 | 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 11 | Go to Step 9 | ||||||||
7 | Inspect for poor connections at the harness connector of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 11 | Go to Step 10 | ||||||||
8 | Repair an open or high resistance in the ground circuit of the rear defog relay. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 11 | -- | ||||||||
9 | Replace the rear defog relay. Refer to Relay Replacement . Did you complete the replacement? | Go to Step 11 | -- | ||||||||
10 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 11 | -- | ||||||||
11 |
Does the DTC reset? | Go to Step 2 | System OK | ||||||||
