B0278
- Body
- Generic (SAE)
Not urgent
Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
HVAC Defrost Door Circuit
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
A fault is detected in the HVAC defrost door actuator circuit; defrost airflow may not engage.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
- Urgency
- Not urgent
- Will it pass emissions
- Not affected
- Check engine light
- Varies
- Warning light or symbol related to the affected system
- Comfort or safety function impaired
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Defrost actuator failed | Very common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- HVAC Defrost Actuator
- HVAC Control Module
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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