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 the 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+ Circuit | 2 | 2 | -- | -- |
Relay Coil B+ Circuit | 2 | 2 | -- | -- |
HVAC B+ Circuit | 2 | 2 | -- | -- |
Rear Defogger Relay Control | B0285 | B0286 | B0286 | -- |
Relay Controlled Output Circuit | 2 | 2 | 3 | -- |
Rear Defogger Switch Signal | 2 | 2 | 2 | -- |
Defog Switch Ground | -- | 1,2 | 1,2 | -- |
Rear Window Defogger Grid Ground | -- | 2 | 2 | -- |
1. HVAC Defogger Indicator Inoperative 2. Rear Defogger Inoperative 3. Rear Defogger Always ON | ||||
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. |
Reference Information
Schematic Reference
Connector End View Reference
Window Systems Connector End Views
Description and Operation
Power Windows Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
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
- Ignition OFF, disconnect the REAR DEFOG relay.
- Ignition OFF, test for less than 1 ohm of resistance between the coil side ground circuit terminal and ground.
- Connect a test lamp between the coil side control circuit terminal and the coil side ground circuit terminal.
- 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 all circuits test normal, test or replace the REAR DEFOG relay.
| ⇒ | If greater than the specified range, test for an open/high resistance. |
| ⇒ | 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. |
Rear Defog Indicator Malfunction
- Ignition OFF, disconnect the harness connector C1 at the HVAC control module.
- Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal 12 and ground.
- Disconnect the REAR DEFOG relay.
- Connect a test lamp between the control circuit terminal 24 and ground.
- 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 all circuits test normal, test or replace the HVAC control module.
| ⇒ | 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. |
Component Testing
Defog Indicator
- Ignition OFF, disconnect the harness at the HVAC control module.
- 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
- Ignition OFF, disconnect the RR DEFOG relay.
- Test for 60-180 ohms of resistance between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- 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 the resistance is 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 BCM and HVAC control module replacement, setup, and programming |
