OBD2 B1344: Rear Defroster Circuit Open
The B1344 code indicates that the Body Control Module (BCM) has detected an open circuit in the power supply to the rear window defroster (heated backlite). When the BCM commands the rear defroster relay to close, it expects to see battery voltage feedback on the output circuit to the rear glass grid. If that voltage is missing, the BCM sets this code, meaning the current path is interrupted somewhere between the relay/BCM and the defroster grid.
1. Commonly Affected Makes
2. Most Common Causes
- Blown rear defroster fuse
- Open circuit in the power wiring between the relay/BCM and the rear glass grid
- Open circuit in the ground connection of the rear glass grid
- Faulty rear defroster relay
- Broken or disconnected filaments in the rear glass grid
- Internal BCM failure in the output driver or monitoring circuit
3. Symptoms You Will Notice
- Rear window defroster does not work
- Rear defroster indicator light on the switch may not illuminate or may flash
4. Step-by-Step Diagnosis
Check and replace any blown fuses related to the rear defroster circuit.
Inspect the rear defroster relay for proper operation and replace if faulty.
Test for battery voltage at the relay output and at the rear glass grid connector.
Check the ground connection of the rear glass grid for continuity.
Visually inspect the rear window grid for broken or disconnected filaments.
If all else is good, test the BCM output driver and replace the BCM if necessary.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is safe to drive. The rear defroster is a convenience feature, not a safety-critical system. However, reduced visibility in cold or humid conditions may be a concern.
How much does it cost to fix?▼
Repair costs typically range from $50 to $300, depending on the cause. A blown fuse or relay is cheap, while a broken grid or BCM replacement can be more expensive.