B0286

DTC B0285 or B0286

Diagnostic Instructions

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



DTC Descriptors
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 RR DEFOG relay. The voltage level should be low while the RR DEFOG relay is de-energized. The voltage will be near system voltage when the BCM energizes the RR DEFOG relay.


Conditions for Running the DTC

Battery voltage must be between 9-16 volts.


Conditions for Setting the DTC

B0285

The BCM detects a short to ground in the relay coil control circuit or a short to ground in the defog indicator control circuit.

B0286

The BCM detects a concurrent short to voltage or an open/high resistance in both of the relay control and the rear defog indicator circuits.


Action Taken When the DTC Sets

The rear window defogger will not operate.


Conditions for Clearing the DTC

* The DTC will be current for as long as the fault is present.
* When the fault is no longer present, the DTC will be a history DTC.
* A history DTC will clear after 50 ignition cycles.



Reference Information
Schematic Reference

Defogger Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Component Connector End Views)
Description and Operation

Rear Window Defogger Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Verification

Ignition ON, command the Rear Defog Relay ON and OFF with a scan tool. The rear window defogger and rear window defogger indicator should turn ON and OFF when changing between the commanded states.


Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
2. Disconnect the RR DEFOG relay.
3. Test for less than 1 ohm between the ground circuit terminal 85 and ground.

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

4. Connect a test lamp between the control circuit terminal 86 and ground circuit terminal 85.
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 commanded 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. Ignition OFF, connect the X2 harness connector at the HVAC control module.
7. Command the rear window defogger 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 or always OFF, replace the HVAC control module.

8. If all circuits test normal, test or replace the RR DEFOG relay.



Component Testing

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

• If 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 30A 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 between terminals 30 and 87.

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




Repair Instructions

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

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