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B0285



DTC B0285 or B0286

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of the diagnostic category.

DTC Descriptor
DTC B0285
- Electric Rear Defrost Circuit Low

DTC B0286
- Electric Rear Defrost Circuit High

Diagnostic Fault Information






Circuit/System Description

The body control module (BCM) monitors the voltage level on the supply voltage circuit of the REAR DEFOG relay. The voltage level should be low while the REAR DEFOG relay is de-energized. The voltage will be near system voltage when the BCM energizes the REAR DEFOG relay.

Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

Conditions for Setting the DTC

B0285

This DTC will set when the BCM detects a low voltage level in the supply circuit of the REAR DEFOG relay when the relay is energized.

B0286

This DTC will set when the BCM detects an open/high resistance in the supply circuit of the REAR DEFOG relay when the relay is energized.

Action Taken When the DTC Sets

* The BCM stores the DTC to memory.
* The rear window defogger will not operate.

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.
* The technician issues a scan tool CLEAR DTCs command.

Circuit/System Verification

1. Command the rear window defogger ON and OFF with the scan tool. The rear window defogger and defogger indicator should turn ON and OFF when changing between the commanded states.

• If the rear window defogger does not turn ON and OFF when changing between the commanded states, refer to Rear Defogger Malfunction.
• If the Defogger Indicator does not illuminate or continuously illuminates, refer to Rear Defog Indicator Malfunction.

Circuit/System Testing

Rear Defogger Malfunction
1. Ignition OFF, disconnect the REAR DEFOG relay.
2. Ignition OFF, test for less than 1 ohm of resistance between the coil side ground circuit terminal and ground.

• If greater than the specified range, test for an open/high resistance.

3. Connect a test lamp between the coil side control circuit terminal and the coil side ground circuit terminal.
4. Command the REAR DEFOG relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit test normal, replace the BCM.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the REAR DEFOG relay.

Rear Defog Indicator Malfunction
1. Ignition OFF, disconnect the harness connector C1 at the HVAC control module.
2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal 12 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Disconnect the REAR DEFOG relay.
4. Connect a test lamp between the control circuit terminal 24 and ground.
5. Ignition ON, command the Rear Defog Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the command states.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

6. If all circuits test normal, test or replace the HVAC control module.

Component Testing

Defog Indicator
1. Ignition OFF, disconnect the harness at the HVAC control module.
2. Install a 5-amp fused jumper wire between circuit terminal 24 and 12 volts. Install a jumper wire between the ground circuit terminal 12 and ground. Verify the Defog indicator illuminates.

• If the Defog Indicator does not illuminate, replace the HVAC control module.

Relay Test
1. Ignition OFF, disconnect the RR DEFOG relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

• If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If not the specified value, replace the relay.

4. Install a 25-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

• If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
* Control Module References for BCM and HVAC control module replacement, setup, and programming. Programming and Relearning
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