B0420
Audio System Internal Failure
The audio head unit reports an internal self-test failure. Symptoms include silent output, frozen display, or repeated reboots of the infotainment system.
- 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.
- Head unit internal faultCommon
- Software update requiredPossible
Parts involved
- Audio Head Unit
- Infotainment Module
B0420 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.