Theft Deterrent Horn Circuit
2018-2025 Fiat Cronos 1.3L I4 Flex Firefly
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
Fiat 124 Spider
2017-2020 1.4L I4 Turbo
Fiat 126p Maluch
1973-2000 0.65L I2 Air-Cooled
Fiat 126p Maluch
1987-2000 0.7L I2 Air-Cooled
Fiat 500
2012-2019 1.4L I4
Fiat 500 Abarth
2012-2019 1.4L I4 Turbo
Fiat 500 BR
2011-2020 1.4L I4 Flex Fire Evo
Fiat 500 PL
2007-2025 1.0L I3 Hybrid FireFly 70
Fiat 500 PL
2007-2025 1.2L I4 Fire 69
Common Questions
What does code B0121 mean on a 2018-2025 Fiat Cronos?
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 Fiat Cronos?
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 2018-2025 Fiat Cronos?
Common causes of B0121 include: Faulty alarm siren, Wiring damage to dedicated siren, BCM siren output failure, Siren connector disconnected.