B0121low severityBody
Theft Deterrent Horn Circuit
on 2003 Audi S6 4.2L V8 · FWD
What this code means
Malfunction in the theft deterrent horn/siren circuit. The alarm horn or siren does not sound during alarm activation.
Symptoms
- No horn sound during alarm
- Alarm triggers silently
- Horn works normally otherwise
- Security light still flashes during alarm
Common causes
- Faulty alarm siren
- Wiring damage to dedicated siren
- BCM siren output failure
- Siren connector disconnected
Diagnostic steps
- Test alarm siren with direct power
- Check wiring from BCM to siren
- Test BCM siren output
- Inspect siren connector
- Verify siren ground
Repair notes
Replace alarm siren or repair wiring. Check for dedicated siren separate from horn.
Other Body codes on this vehicle
B0001
Driver Frontal Stage 1 Deployment Control
B0002
Driver Frontal Stage 2 Deployment Control
B0003
Passenger Frontal Stage 1 Deployment Control
B0004
Passenger Frontal Stage 2 Deployment Control
B0005
Driver Knee Airbag Deployment Circuit
B0006
Passenger Knee Airbag Deployment Circuit
B0010
Driver Side Airbag Deployment
B0011
Driver Side Airbag Deployment Circuit Open
B0012
Driver Side Airbag Deployment Circuit Short to Ground
B0013
Driver Side Airbag Deployment Circuit Short to Battery