B0420Audio System Internal Failure
- Generic OBD-II code · Body
- How the car detects it
- No public J2012 list carries B0420 with this meaning, and no carmaker describes an audio-system fault under it. The one documented use is unrelated: Saab files B0420 06 in the 9-3 (2003–2012) climate control as an open or grounded circuit to the right air-mix flap motor, which upsets temperature control. Read literally, the title points to a fault inside the head unit, the part that feeds every speaker channel. Saab's 2011 9-5 shows how such units judge their outputs: the radio stores B1025–B1055 for a shorted or open speaker line and mutes only that channel. Klippel describes how the DSP, amplifier and microphones already fitted in a car could run a self-test of the whole system. Lost bus contact with the radio belongs under U0184.
- What you may notice
- No sound from any speaker, or the radio restarts by itself
- Head unit freezes or ignores its buttons
- Code stored together with other infotainment faults
- Likely causes
- LikelyInternal electronics or software of the head unit faulty
- PossibleLow or unstable supply voltage or poor ground at the head unit
- RareUnit overheated because of blocked ventilation behind the dash
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.