OBD2 B1348: Rear Defogger Relay Circuit Open
The B1348 code indicates that the Body Control Module (BCM) or climate control module has detected an open circuit in the rear defogger (heated backlite) relay circuit. This relay controls power to the rear window heating element. An open circuit means there is a break in the electrical path, preventing the relay from activating or the control signal from reaching it, resulting in the rear defogger system not working. The code is typically set during the vehicle's comfort system self-test when the module attempts to energize the relay but does not detect the expected current or voltage feedback.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or internally damaged rear defogger relay
- Open or broken wiring between the control module and the relay
- Corroded, loose, or disconnected relay connector
- Blown fuse in the rear defogger relay circuit
- Body Control Module (BCM) with internal failure in relay control
- Poor ground connection in the relay circuit
3. Symptoms You Will Notice
- Rear window defogger does not work
- Rear defogger indicator light on the switch may not illuminate or may flash
4. Step-by-Step Diagnosis
Check the rear defogger relay fuse and replace if blown.
Inspect the relay for signs of damage or corrosion; test relay coil resistance and switching function.
Verify voltage and ground at the relay socket with a multimeter.
Check for continuity in the wiring between the BCM and the relay connector.
If all else is normal, test the BCM output to the relay; replace BCM if faulty.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive, but the rear defogger will not work, which can reduce visibility in cold or humid conditions.
How much does it cost to fix?▼
Repair costs typically range from $50 to $200 for relay or fuse replacement, up to $500 or more if the BCM needs replacement.