OBD-II code · Body
B0278 HVAC Defrost Door Circuit
A fault is detected in the HVAC defrost door actuator circuit; defrost airflow may not engage.
Is it safe to drive with B0278?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyDefrost actuator failed
Symptoms
- Warning light or symbol related to the affected system
- Comfort or safety function impaired
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.8–3 h
- Emissions test
- Usually unaffected
- Parts involved
- HVAC Defrost Actuator, HVAC Control Module
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.