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Home / DTC / B1726 — Immob-too much challenge receive

B1726 — Immob-too much challenge receive

Detailed page for trouble code B1726.

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Code

B1726

MITSUBISHI B — Body

Immob-too much challenge receive

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

Causes

  • Faulty or damaged transponder key (weak/failed chip or incorrect key)
  • Damaged or misaligned immobilizer antenna coil (key reader) near the ignition
  • Intermittent or open wiring/connectors between antenna, immobilizer ECU and engine ECU
  • Low vehicle battery or low key fob battery causing communication errors
  • Noise or interference on the vehicle communication bus (CAN/LIN) or radio-frequency interference near the antenna
  • Faulty immobilizer control module or engine control module software/firmware fault

Symptoms

  • Engine cranks but does not start, or crank is disabled
  • Security/immobilizer indicator lamp illuminated or flashing
  • Intermittent no-start condition dependent on key or position
  • No crank and vehicle locked out from starting
  • Related DTCs for communication faults (CAN/LIN) or other immobilizer codes present

What to check

  • Read and record all stored DTCs (immobilizer and communication codes) and freeze frame data
  • Confirm behavior with known-good/master key and spare key(s)
  • Inspect ignition key and key fob for physical damage; check key fob battery
  • Visual inspection of antenna coil around ignition switch for damage or looseness
  • Inspect wiring, connectors and grounds between antenna, immobilizer ECU and ECM for corrosion, continuity and secure fit
  • Check vehicle battery voltage and charging system

Signal parameters

  • Antenna coil excitation frequency: nominal ~125 kHz (verify presence of RF when key near coil)
  • Transponder response: presence/absence of valid transponder ID and checksum
  • Number of challenge/response attempts and failure count recorded by immobilizer ECU
  • Battery supply to immobilizer/antenna: nominal ~12 V (check for drops during cranking)
  • CAN/LIN bus voltages and error counters (dominant/recessive levels, bus error frames)
  • Ground continuity and resistance at immobilizer ECU and antenna ground

Diagnostic algorithm

  1. Use a diagnostic scan tool to read all immobilizer and communication DTCs; note freeze frame and clear codes to see if they return.
  2. Attempt vehicle start with the primary key and a known-good spare/master key. If spare works, suspect the primary key transponder.
  3. Inspect the physical condition of the keys and key fob battery; replace key battery if weak and retest.
  4. Visually inspect the immobilizer antenna coil and connector at the ignition barrel; check for damage, looseness or corrosion.
  5. With ignition off, check continuity and resistance of wiring between antenna, immobilizer ECU and engine ECU; repair any open or high-resistance circuits.
  6. Measure supply voltage to immobilizer and antenna while attempting start; look for voltage drops or irregularities.
  7. Monitor transponder/immobilizer signals with an appropriate tool (RF detector or oscilloscope) to confirm antenna excitation and transponder response.
  8. Scan CAN/LIN bus for errors and lost communication events. Repair bus issues if present (terminators, wiring shorts, module faults).
  9. Temporarily disable or disconnect aftermarket alarm/remote-start modules and retest to eliminate interference.
  10. If wiring and keys check good but fault persists, perform immobilizer ECU key reprogramming/relearn per manufacturer procedure; if unsuccessful, consider replacing immobilizer ECU or antenna coil and retest.
  11. After repairs, clear codes and confirm normal operation over multiple start cycles; re-scan to ensure B1726 does not return.

Likely causes

  • Damaged transponder in the key (most common)
  • Antenna coil fault or poor connector/ground at the antenna
  • Corroded/loose wiring between immobilizer ECU and ignition/ECM
  • Communication bus error preventing valid challenge/response exchange

Fault status

⚠️ Status
Immobilizer control unit logged excessive or invalid challenge/response receipts; key authorization failed or communication fault detected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

B1720 B1725 P1621 U0100 U0073
406

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