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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B0285 Electric Rear Defrost Circuit Low
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.
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Listen for an audible click when the REAR DEFOG relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
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Verifies that the BCM is providing ground input to the REAR DEFOG relay.
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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 Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
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 | |
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 7 | Go to Step 9 |
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 | Replace the BCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming. Did you complete the replacement? | Go to Step 12 | -- |
12 |
Does the DTC reset? | Go to Step 2 | System OK |
