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Home / DTC / B2401 — KOS key ID not registered

B2401 — KOS key ID not registered

Detailed page for trouble code B2401.

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Code

B2401

MITSUBISHI B — Body

KOS key ID not registered

Brand: MITSUBISHI
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Key transponder ID not programmed or erased from immobilizer memory
  • Faulty or damaged key/transponder
  • Low or dead key battery (affecting RF/ID transmission)
  • Antenna coil (immobilizer reader) failure or poor connection
  • Wiring or connector fault between antenna, BCM and immobilizer module
  • BCM/immobilizer module software/corruption or hardware failure

Symptoms

  • Engine will not crank or start with affected key
  • Push-button start does not respond or displays a ‘key not recognized’ message
  • Immobilizer or key warning lamp illuminated or flashing
  • Vehicle may allow accessory power but not engine start
  • Other keys (if present) may work or also be unrecognized

What to check

  • Confirm presence of DTC B2401 and note freeze-frame/failure records with a diagnostic scan tool
  • Attempt start with all known keys to determine if problem is key-specific
  • Check key battery voltage and replace if low
  • Scan for related codes in BCM, immobilizer and engine control modules
  • Use diagnostic tool to read list of registered key IDs in immobilizer memory
  • Inspect antenna coil/reader and its connector near the start button for damage/corrosion

Signal parameters

  • Registered Key ID list (stored immobilizer IDs)
  • Detected transponder response / ID read during start attempt
  • Key battery voltage (V)
  • Antenna coil supply voltage and coil resistance (ohms)
  • Immobilizer/BCM CAN communication status
  • Immobilizer status flags (locked/unlocked/program mode)

Diagnostic algorithm

  1. Retrieve and record DTC B2401 and related codes from BCM/immobilizer using OEM diagnostic tool.
  2. Confirm symptom: try starting with all available keys and note which keys are accepted or rejected.
  3. Check and, if necessary, replace the coin battery in the key. Re-test key recognition.
  4. With diagnostic tool, read the immobilizer’s stored key ID list. Verify whether the suspect key’s ID is present.
  5. If key ID is absent and the key is known-good, attempt key registration/programming per manufacturer procedure (use Mitsubishi MUT-III or equivalent).
  6. If programming fails or the tool reports communication error, inspect antenna coil and connector at the start/reader: check for correct supply voltage and measure coil resistance against spec.
  7. Check wiring and connectors between antenna, BCM and immobilizer module for continuity, corrosion, or damage. Repair as needed.
  8. Scan CAN network and module communications; verify BCM and immobilizer module respond and have correct software. Reflash or replace module only after confirming other causes.
  9. After registering key or repairing hardware, clear DTCs and perform multiple start tests with each key. Confirm no reoccurrence.
  10. If the fault persists after these steps, consider replacing the immobilizer/BCM and have dealer-level programming performed.

Likely causes

  • Key was recently replaced or cloned and not programmed
  • Vehicle battery replacement or BCM replacement cleared key memory
  • Key battery exhausted and transponder not responding
  • Antenna coil/reader located near the start button is defective or disconnected
  • Faulty immobilizer/BCM not storing or reading key IDs

Fault status

⚠️ Status
Key transponder ID not found in immobilizer memory; key not registered.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B2400 B2402 B2403 B2470 B2799
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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Code

B2401

Other B — Body

Audio Tape Deck Mechanism Fault

Brand: Other
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Key transponder ID not programmed or erased from immobilizer memory
  • Faulty or damaged key/transponder
  • Low or dead key battery (affecting RF/ID transmission)
  • Antenna coil (immobilizer reader) failure or poor connection
  • Wiring or connector fault between antenna, BCM and immobilizer module
  • BCM/immobilizer module software/corruption or hardware failure

Symptoms

  • Engine will not crank or start with affected key
  • Push-button start does not respond or displays a ‘key not recognized’ message
  • Immobilizer or key warning lamp illuminated or flashing
  • Vehicle may allow accessory power but not engine start
  • Other keys (if present) may work or also be unrecognized

What to check

  • Confirm presence of DTC B2401 and note freeze-frame/failure records with a diagnostic scan tool
  • Attempt start with all known keys to determine if problem is key-specific
  • Check key battery voltage and replace if low
  • Scan for related codes in BCM, immobilizer and engine control modules
  • Use diagnostic tool to read list of registered key IDs in immobilizer memory
  • Inspect antenna coil/reader and its connector near the start button for damage/corrosion

Signal parameters

  • Registered Key ID list (stored immobilizer IDs)
  • Detected transponder response / ID read during start attempt
  • Key battery voltage (V)
  • Antenna coil supply voltage and coil resistance (ohms)
  • Immobilizer/BCM CAN communication status
  • Immobilizer status flags (locked/unlocked/program mode)

Diagnostic algorithm

  1. Retrieve and record DTC B2401 and related codes from BCM/immobilizer using OEM diagnostic tool.
  2. Confirm symptom: try starting with all available keys and note which keys are accepted or rejected.
  3. Check and, if necessary, replace the coin battery in the key. Re-test key recognition.
  4. With diagnostic tool, read the immobilizer’s stored key ID list. Verify whether the suspect key’s ID is present.
  5. If key ID is absent and the key is known-good, attempt key registration/programming per manufacturer procedure (use Mitsubishi MUT-III or equivalent).
  6. If programming fails or the tool reports communication error, inspect antenna coil and connector at the start/reader: check for correct supply voltage and measure coil resistance against spec.
  7. Check wiring and connectors between antenna, BCM and immobilizer module for continuity, corrosion, or damage. Repair as needed.
  8. Scan CAN network and module communications; verify BCM and immobilizer module respond and have correct software. Reflash or replace module only after confirming other causes.
  9. After registering key or repairing hardware, clear DTCs and perform multiple start tests with each key. Confirm no reoccurrence.
  10. If the fault persists after these steps, consider replacing the immobilizer/BCM and have dealer-level programming performed.

Likely causes

  • Key was recently replaced or cloned and not programmed
  • Vehicle battery replacement or BCM replacement cleared key memory
  • Key battery exhausted and transponder not responding
  • Antenna coil/reader located near the start button is defective or disconnected
  • Faulty immobilizer/BCM not storing or reading key IDs

Fault status

⚠️ Status
Key transponder ID not found in immobilizer memory; key not registered.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B2400 B2402 B2403 B2470 B2799
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