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Home / DTC / B29ED — Key switch signal:close cycle

B29ED — Key switch signal:close cycle

Detailed page for trouble code B29ED.

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Code

B29ED

MITSUBISHI B — Body

Key switch signal:close cycle

Brand: MITSUBISHI
Type: B — Body
Views: UK: 14 EN: 17 RU: 17
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Page language: EN

Causes

  • Worn, dirty or mechanically failing ignition/key switch
  • Intermittent open or short in ignition switch wiring or connectors
  • Corroded/loose connector or poor ground at harness or body ECU
  • Aftermarket alarm/immobilizer or keyless entry module interfering with signal
  • Faulty body/BCM or engine/ECU input circuit
  • Software glitch or incorrect module configuration

Symptoms

  • Intermittent no‑start or crank/no‑start conditions
  • Accessory or ignition functions operating intermittently
  • Battery drain if switch is stuck or parasitic feed present
  • Starter engages unexpectedly or fails to engage
  • Illumination of security/immobilizer warning lamp
  • Related modules reporting communication or input faults

What to check

  • Retrieve stored codes and freeze‑frame data; note key position and battery voltage when code set
  • Visually inspect ignition switch, key cylinder, connectors and wiring harness for damage, corrosion or loosened terminals
  • Check battery state and main power/ground integrity for body and engine control modules
  • Backprobe ignition switch harness and measure voltage while cycling key through OFF/ACC/ON/START
  • Wiggle test wiring and connectors while monitoring signal for intermittent changes
  • Scan for related security/immobilizer or communications trouble codes

Signal parameters

  • OFF position: approx. 0 V (no feed) on ignition input circuit
  • ON/ACC/START: near battery voltage (approx. 12–14 V) with key in that position
  • Continuity across closed contacts: low resistance (typically < 1 ohm) between relevant terminals
  • No rapid oscillation or chatter when key is held steady; switch bounce should be short (< 50–200 ms)
  • No voltage spikes, drops or intermittent opens during turn-to-start or key return

Diagnostic algorithm

  1. Safety: ensure vehicle is secure, battery stable and you have proper immobilizer code/access if required.
  2. Read and record all DTCs and freeze‑frame data. Note when and under what conditions B29ED appears.
  3. Visually inspect the key cylinder, ignition switch assembly and related harness for damage, corrosion or aftermarket devices.
  4. With a multimeter, backprobe the ignition switch input at the switch connector. Verify voltage transitions for each key position (OFF/ACC/ON/START).
  5. Perform a wiggle and continuity test: move harness and connectors while watching signal for intermittent opens or shorts.
  6. If intermittent is suspected, capture the signal with an oscilloscope while cycling the key to detect bounce, chatter, or noise signatures.
  7. Inspect/measure connector pins and ground points. Repair corroded pins, restore grounds, and secure connectors.
  8. If wiring and switch check good, verify no aftermarket immobilizer or alarm is causing interference; temporarily disconnect if present and retest.
  9. If the switch is mechanically degraded or signal remains abnormal, replace the ignition/key switch or lock cylinder per factory procedure.
  10. If fault persists after switch and wiring repairs, test/replace the body ECU or other modules only after confirming proper inputs and communications.
  11. Clear codes and retest vehicle through repeated key cycles and drive test to ensure fault does not return.

Likely causes

  • Ignition switch contacts worn or sticking (mechanical failure)
  • Broken wire, damaged insulation or pin pushed out in connector to switch
  • Short to battery or ground causing multiple rapid open/close detections
  • Poor ground causing noisy signal
  • Aftermarket immobilizer or wiring added incorrectly

Fault status

⚠️ Status
Key switch signal: abnormal closed-cycle detected (intermittent/oscillating or out-of-range closure)
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B29EA B29EB B29EC B29EE U0100 P0562
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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