Theft Deterrent Horn Circuit
2018-2018 Lincoln MKX 2.7L EcoBoost V6
The 2018 Lincoln MKX is equipped with a 2.7L V6 turbocharged gasoline engine. 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
- B0001Driver Frontal Stage 1 Deployment Control
- B0002Driver Frontal Stage 2 Deployment Control
- B0002Driver Frontal Stage 2 Deployment Control
- B0003Passenger Frontal Stage 1 Deployment Control
- B0003Passenger Frontal Stage 1 Deployment Control
- B0004Passenger Frontal Stage 2 Deployment Control
- B0004Passenger Frontal Stage 2 Deployment Control
- B0005Driver Knee Airbag Deployment Circuit
- B0005Driver Knee Airbag Deployment Circuit
B0121 on Other Vehicles
Lincoln Aviator
2003-2003 4.6L V8 DOHC
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2004-2004 4.6L V8 DOHC
Lincoln Aviator
2005-2005 4.6L V8 DOHC
Lincoln Aviator
2020-2020 3.0L Twin-Turbo V6
Lincoln Aviator
2020-2020 3.0L V6 Twin Turbo
Lincoln Aviator
2020-2020 3.0L V6 Twin Turbo Hybrid
Lincoln Aviator
2021-2021 3.0L Twin-Turbo V6
Lincoln Aviator
2021-2021 3.0L V6 Twin Turbo
Common Questions
What does code B0121 mean on a 2018-2018 Lincoln MKX?
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 Lincoln MKX?
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 2018-2018 Lincoln MKX?
Common causes of B0121 include: Faulty alarm siren, Wiring damage to dedicated siren, BCM siren output failure, Siren connector disconnected.
Last updated: March 2026