B0278
HVAC Defrost Door Circuit
A fault is detected in the HVAC defrost door actuator circuit; defrost airflow may not engage.
- Check engine light: Not always
- Emissions related: No
- Repair difficulty: medium
Symptoms
- Warning light or symbol related to the affected system
- Comfort or safety function impaired
Common causes
Ordered by how often each turns out to be the cause.
- Defrost actuator failedCommon
Parts involved
- Hvac Defrost Actuator
- Hvac Control Module
B0278 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.