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2018 TESLA MODEL 3
Performance Dual Motor AWD•AWD•AUTOMATIC•ev
18 active safety recalls on this vehicle — view recalls
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Repairs0Labor322Torque4793Fluid5DTC726Battery1Maintenance0Recalls18
B0121low severityBody

Theft Deterrent Horn Circuit

on 2018 Tesla Model 3 Performance Dual Motor AWD · AWD

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

  1. Test alarm siren with direct power
  2. Check wiring from BCM to siren
  3. Test BCM siren output
  4. Inspect siren connector
  5. Verify siren ground

Repair notes

Replace alarm siren or repair wiring. Check for dedicated siren separate from horn.

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🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Mechanic · 20+ years. Spot an error? Use the Help link above — a human reads every report.
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