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2002 BMW 525IT E39
2.5L I6 M54 Touring•RWD•AUTOMATIC•gas•M54B25
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Repairs0Labor478Torque644Fluid8DTC2024Battery1Maintenance0Recalls0
B0101high severityBody

Immobilizer Transponder Signal Not Detected

on 2002 BMW 525iT E39 2.5L I6 M54 Touring · RWD

What this code means

The immobilizer system cannot detect the transponder signal from the key. The engine will not start.

Symptoms

  • Engine cranks but will not start
  • Security light flashing
  • Key symbol on dashboard
  • No-start condition

Common causes

  • Dead key battery (smart key)
  • Faulty transponder chip in key
  • Damaged antenna ring around ignition
  • Interference from other transponder keys
  • Key handle cracked exposing transponder to damage

Diagnostic steps

  1. Try different registered key
  2. Hold key closer to ignition/start button
  3. Check for key battery (if applicable)
  4. Test antenna ring with known-good key
  5. Scan immobilizer codes

Repair notes

Replace key battery or have new key programmed. Replace antenna ring if faulty.

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