Theft Deterrent Horn Circuit
2019-2019 Tesla Model 3 Performance Dual Motor AWD
The 2019 Tesla Model 3 is equipped with a Performance Dual Motor AWD engine (AWD). Below you'll find detailed b0121 diagnostic code information including labor time estimates, cost ranges, and technician notes specific to this engine configuration.
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
- B0007Rear Left Side Airbag Deployment Circuit
- B0008Rear Right Side Airbag Deployment Circuit
- B0009Rear Center Airbag Deployment Circuit
- B0010Driver Side Airbag Deployment
B0121 on Other Vehicles
Tesla Cybertruck
2024-2024 Cyberbeast Tri Motor AWD
Tesla Cybertruck
2024-2024 Dual Motor AWD
Tesla Cybertruck
2024-2024 Single Motor RWD
Tesla Model 3
2017-2017 Long Range Dual Motor AWD
Tesla Model 3
2017-2017 Performance Dual Motor AWD
Tesla Model 3
2017-2017 Standard Range Plus Single Motor RWD
Tesla Model 3
2018-2018 Long Range Dual Motor AWD
Tesla Model 3
2018-2018 Performance Dual Motor AWD
Common Questions
What does code B0121 mean on a 2019-2019 Tesla Model 3?
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 Tesla Model 3?
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 2019-2019 Tesla Model 3?
Common causes of B0121 include: Faulty alarm siren, Wiring damage to dedicated siren, BCM siren output failure, Siren connector disconnected.
Last updated: March 2026