B0121
Theft Deterrent Horn Circuit
1999-2000 BMW 528iT E39 2.8L I6 🇩🇪
Low SeverityBody
Description
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.
Related Codes
Other Body Codes
- B0001Driver Frontal Stage 1 Deployment Control
- B0002Driver Frontal Stage 2 Deployment Control
- B0003Passenger Frontal Stage 1 Deployment Control
- B0004Passenger Frontal Stage 2 Deployment Control
- B0005Driver Knee Airbag Deployment Circuit
- B0006Passenger Knee Airbag Deployment Circuit
- B0010Driver Side Airbag Deployment
- B0011Driver Side Airbag Deployment Circuit Open
- B0012Driver Side Airbag Deployment Circuit Short to Ground
- B0013Driver Side Airbag Deployment Circuit Short to Battery
B0121 on Other Vehicles
Common Questions
What does code B0121 mean on a 1999-2000 BMW 528iT E39?
B0121 stands for "Theft Deterrent Horn Circuit". Malfunction in the theft deterrent horn/siren circuit. The alarm horn or siren does not sound during alarm activation.
What are the symptoms of B0121 on a BMW 528iT E39?
Common symptoms of B0121 include: No horn sound during alarm, Alarm triggers silently, Horn works normally otherwise, Security light still flashes during alarm.
What causes B0121 on a 1999-2000 BMW 528iT E39?
Common causes of B0121 include: Faulty alarm siren, Wiring damage to dedicated siren, BCM siren output failure, Siren connector disconnected.