Diagnostic Routine F

Diagnostic Routine F

Diagnostic Overview

The Defrost System Does Not Shut Off Automatically

Refer to Wiring Diagram Set 56 for schematic and connector information Electrical Diagrams.

Normal Operation and Fault Conditions

The HVAC (Heating, Ventilation, and Air Conditioning) module deactivates the rear window defrost relay whenever the ignition is turned OFF, the rear window defrost switch is pressed (while the defrost system is active) or after a 15 minute timer has elapsed. REFER to Rear Window Defrost .

If the defrost system is active with the ignition in the OFF position, the fault could be an inoperative rear window defrost relay (contacts stuck closed) or a short to voltage in the rear window defrost grid voltage circuit.

If the defrost system is active only when the ignition is in the ON position, the fault could be a short to ground in the rear window defrost relay control circuit or a HVAC (Heating, Ventilation, and Air Conditioning) module concern (driver active all the time).

DTC Fault Trigger Conditions






Visual Inspection and Diagnostic Pre-checks

- Visually inspect the rear window defrost relay.

Pinpoint Test

1. CHECK FOR A SHORT TO VOLTAGE IN THE REAR WINDOW DEFROST GRID POWER CIRCUIT

1. Disconnect: Rear Window Defrost Relay.

2. Disconnect: Rear Window Defrost Grid C402A.

3. Ignition ON.

4. Measure:





Is any voltage present?








2. CHECK THE REAR WINDOW DEFROST RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND
NOTICE: The following step uses a test light to simulate normal circuit loads. Use only the test light recommended in the Special Tools table at the beginning. To avoid connector terminal damage, use the Flex Probe Kit for the test light probe connection to the vehicle. Do not use the test light probe directly on any connector.

1. Start the engine.

2. Measure:





Does the test light illuminate?








3. CHECK THE REAR WINDOW DEFROST RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND WITH THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE DISCONNECTED
NOTICE: The following step uses a test light to simulate normal circuit loads. Use only the test light recommended in the Special Tools table at the beginning. To avoid connector terminal damage, use the Flex Probe Kit for the test light probe connection to the vehicle. Do not use the test light probe directly on any connector.

1. Ignition OFF.

2. Disconnect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

3. Ignition ON.

4. Measure:





Does the test light illuminate?








4. CHECK FOR CORRECT HVAC (Heating, Ventilation, and Air Conditioning) MODULE OPERATION

1. Inspect the HVAC (Heating, Ventilation, and Air Conditioning) module connectors.

2. Repair:

- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins as necessary
- pushed-out-pins - install new pins as necessary

3. Reconnect the HVAC (Heating, Ventilation, and Air Conditioning) module connectors. Make sure they seat and latch correctly.

4. Operate the system and determine if the concern is still present.

Is the concern still present?