B0420 code meaning
Audio System Internal Failure
What B0420 means
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.
B0420 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0420
- 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
Common causes of B0420
- Most likelyInternal electronics or software of the head unit faulty
- PossibleLow or unstable supply voltage or poor ground at the head unit
- Less likelyUnit overheated because of blocked ventilation behind the dash
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Audio head unitInfotainment module
What each part of B0420 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 20 | The exact fault in that area. |
What to do next
- Note B0420 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0420
What does B0420 mean?
B0420 means "Audio System Internal Failure". No public J2012 list carries B0420 with this meaning, and no carmaker describes an audio-system fault under it. It is a generic code, so it means the same on every make.
Is it safe to drive with B0420?
B0420 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0420 fail an emissions test?
B0420 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0420 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will B0420 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.