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Home / DTC / B2405 — STL.unit comm.(rolling code)

B2405 — STL.unit comm.(rolling code)

Detailed page for trouble code B2405.

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Code

B2405

MITSUBISHI B — Body

STL.unit comm.(rolling code)

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

Causes

  • Faulty steering lock (STL) unit or internal electronics
  • Damaged or loose connector(s) at the STL unit
  • Wiring harness damage (short/open/ground) between STL and BCM/immobilizer/ECU
  • Low vehicle or key battery voltage during handshake
  • Broken or unprogrammed key transponder (rolling-code mismatch)
  • Aftermarket security or RF interference disrupting rolling-code exchange

Symptoms

  • Immobilizer/security warning light on or flashing
  • Engine cranks but will not start, or starter disabled
  • Key may not turn or steering lock remains engaged
  • Intermittent no-start or start delay tied to key use
  • Multiple communication or security-related DTCs present in scan tool

What to check

  • Read all stored and pending DTCs (including U-codes) and note freeze-frame data
  • Verify vehicle battery voltage (should be ~12–14 V) and condition
  • Visually inspect STL unit connector and wiring for corrosion, damage, or loose pins
  • Check fuses and ground points for the STL / immobilizer circuits
  • Attempt start with a known-good, programmed key (spare key) to rule out key/transponder
  • Use a scan tool to monitor communication messages between STL, BCM and immobilizer during a start attempt

Signal parameters

  • Power supply to STL: ~11–14 V with engine off and cranking
  • Ground: continuity to chassis, low resistance (
  • Communication: rolling-code handshake messages visible on diagnostic tool when starting or unlocking (module-specific timing)
  • Bus signal presence: CAN/LIN frames from/to STL/BCM present during start attempt (module dependent)
  • No sustained short to battery or short to ground on STL data lines

Diagnostic algorithm

  1. Connect a professional scan tool and read all DTCs; save data and note time stamps.
  2. Verify vehicle and key battery voltages; charge or replace if low.
  3. Inspect STL unit connectors, wiring harness and ground points; repair any damage or corrosion.
  4. Check related fuses and power supply to the STL unit; repair if faulty.
  5. With scan tool, monitor communication on the network (CAN/LIN) while attempting ignition; confirm whether STL messages are transmitted and whether rolling-code handshake occurs.
  6. Try starting with a known-good programmed key. If spare key works, suspect key/transponder or rolling-code sync.
  7. If no communication from STL, verify power/ground at the unit and consider bench or in-vehicle replacement following OEM procedures.
  8. If STL replaced or reprogrammed, ensure correct module coding/rolling-code learning procedure is performed per manufacturer instructions.
  9. Clear codes and retest multiple start cycles to confirm repair; if intermittent, perform wiggle tests on harness and re-check connectors.

Likely causes

  • Intermittent connector/circuit causing lost packets during rolling-code exchange
  • Key not properly programmed or rolling-code out of sync
  • Failed STL actuator or internal controller
  • Corroded antenna/coil around ignition or key reader preventing transponder read
  • Aftermarket alarm or RF device causing interference

Fault status

⚠️ Status
STL unit communication error — rolling-code handshake failed or lost (security/immobilizer communication fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 2.5 hours

Similar codes

B2400 B2401 B2402 B2410 U0100 U0121
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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