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Home / DTC / B29B8 — Door lock signal:close cycle

B29B8 — Door lock signal:close cycle

Detailed page for trouble code B29B8.

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Code

B29B8

MITSUBISHI B — Body

Door lock signal:close cycle

Brand: MITSUBISHI
Type: B — Body
Views: UK: 15 EN: 19 RU: 22
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty door lock actuator (sticking or intermittent)
  • Defective door lock switch or keyless entry switch
  • Damaged wiring, pinched harness or poor connector contact between door and BCM
  • Corrosion or water intrusion in door connector or actuator
  • Weak battery or low supply voltage during lock cycle
  • Body Control Module (BCM) or door module fault or software anomaly

Symptoms

  • Door does not lock or unlock when commanded (intermittent or complete failure)
  • One door fails to respond while others operate normally
  • Clicking or no sound from door lock when operating switch/remote
  • Malfunction indicator or body module message for door lock
  • Locks operate inconsistently or require multiple attempts

What to check

  • Read all stored DTCs and freeze frame data with a capable scan tool; note which door(s) reported
  • Attempt to reproduce the fault: cycle lock/unlock with key fob, interior switch and door switch
  • Visually inspect door harness, grommet and connector for damage, corrosion or water
  • Listen for actuator operation; compare sound/response of suspect door to a working door
  • Check battery voltage while operating locks (should be ~12–14 V); rule out low voltage
  • Inspect fuses and relays for the central locking circuit

Signal parameters

  • Lock command: switched between battery voltage and ground (0–12 V range) depending on system design
  • Expected change: clear ON/OFF transition when lock/unlock is commanded; no stuck or noisy signal
  • Pulse/operation duration: actuator drive typically completes within 0.5–2 seconds
  • Continuity/resistance: actuator coil resistance should be stable and similar to the same-model door (measure and compare)
  • Communication: CAN/LIN messages present for lock command when using remote or switch (check with a bus analyzer or scan tool)

Diagnostic algorithm

  1. Connect an OEM-capable scan tool. Read and record DTCs and any freeze frame/data. Note which door is affected and any related codes.
  2. Try to reproduce the fault with the scan tool monitoring door lock inputs/outputs and BCM status. Operate all lock inputs (fob, interior switch, manual) and observe signal changes.
  3. Visually inspect the affected door’s wiring, grommet in the hinge area and connectors for chafing, corrosion or water entry.
  4. Perform a functional check: command lock/unlock and listen/observe the actuator. Compare to a known-good door to isolate mechanical vs electrical issue.
  5. Measure voltage at the actuator connector while commanding a lock: verify proper supply and switching. If no switching, trace back to door module/BCM connector.
  6. Check actuator coil resistance and compare to spec or other doors. High or open resistance indicates a faulty actuator.
  7. Wiggle test wiring while operating the lock to reveal intermittent connections. Repair or replace damaged wiring/harness as needed.
  8. If wiring and actuator test good, inspect/replace the door lock switch or inspect keyless entry receiver input to the BCM.
  9. If electrical inputs to BCM are present but actuator still not driven, investigate BCM outputs and related relays; check for software updates or BCM faults.
  10. After repairs, clear codes and perform several lock/unlock cycles to confirm the fault does not return and monitor live data for correct signal cycles.

Likely causes

  • Worn or seized door lock actuator in the affected door
  • Loose or corroded connector at the door harness or actuator
  • Damaged wiring in the door jamb (flex area) causing intermittent open/short
  • Faulty door lock switch or remote receiver not sending a complete close pulse

Fault status

⚠️ Status
Door lock close signal cycle fault — incomplete or missing lock signal detected by body control system.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B29B6 B29B7 B29B9 B2920 U0140 U0131
203

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