Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC B0285: Electric Rear Defrost Circuit LowDTC B0286: Electric Rear Defrost Circuit High
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Relay Switch B+ | 1 | 1 | -- | -- |
Rear Defog Switch Signal | 2 | 1 | 1 | -- |
Rear Defog Relay Control | B0285 | B0286 | B0286 | -- |
Rear Defogger Control | 1 | 1 | 2 | -- |
Rear Defog Indicator Control | B0285 | B0286 | B0286 | -- |
HVAC Control Module Ground | -- | 1 | 1 | -- |
Relay Coil Ground | -- | B0286 | 1 | -- |
Rear Window Defogger Grid Ground | -- | 1 | 1 | -- |
1. Rear Defogger Inoperative 2. Rear Defogger Always ON | ||||
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
Connector End View Reference
Description and Operation
Rear Window Defogger Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References 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
- Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
- Disconnect the RR DEFOG relay.
- Test for less than 1 ohm between the ground circuit terminal 85 and ground.
- Connect a test lamp between the control circuit terminal 86 and ground circuit terminal 85.
- 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.
- Ignition OFF, connect the X2 harness connector at the HVAC control module.
- 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 all circuits test normal, test or replace the RR DEFOG relay.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | If the test lamp is always ON or always OFF, replace the HVAC control module. |
Component Testing
- Ignition OFF, disconnect the RR DEFOG relay.
- Test for 60-180 ohms between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- 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 not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for HVAC control module and BCM replacement, setup, and programming |
