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Home / DTC / B2102 — IG SW start POS.circuit high

B2102 — IG SW start POS.circuit high

Detailed page for trouble code B2102.

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Code

B2102

MITSUBISHI B — Body

IG SW start POS.circuit high

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

Causes

  • Faulty ignition switch (START contact stuck or internally shorted)
  • Short to battery voltage on the START circuit (wiring damaged/ chafed)
  • Poor or corroded connector terminal at ignition switch or ECU/BCM
  • Shorted or incorrect aftermarket immobilizer/remote start installation
  • Faulty body control module / ECU input circuit
  • Blown/incorrect fuse or relay fault affecting circuit reference

Symptoms

  • Starter may crank unexpectedly or behave erratically
  • Vehicle may not allow proper starting or cranking depending on safety interlocks
  • DTC illumination or stored body/PCM faults related to ignition input
  • Intermittent start/no-start or inability to shut off accessory circuits

What to check

  • Retrieve stored DTCs and freeze-frame data with a scan tool
  • Inspect ignition switch, connectors, and harness for damage or corrosion
  • Visually inspect for aftermarket immobilizer/remote-start wiring
  • Check fuses and relays related to ignition/start circuit
  • Backprobe START circuit at ignition switch and control module with key in OFF/ON/START
  • Check for continuity to battery voltage and for shorts to battery

Signal parameters

  • Expected: START circuit should be near 0 V (or open) in OFF/ON (run) and show battery voltage (~12 V) only while key is in START/cranking
  • Measured: circuit remains at high (battery) voltage when key is not in START or signal does not change state during crank
  • ECU input should toggle according to key position when monitored with scan tool or voltmeter

Diagnostic algorithm

  1. Connect a scan tool, record DTCs and any related codes/freeze data. Note vehicle conditions when code set.
  2. Visually inspect the ignition switch harness, connectors, grounding points, and related fuse/relay boxes for damage, corrosion, or loose terminals.
  3. Confirm correct battery voltage and health. Low/unstable battery can cause false readings.
  4. With ignition OFF, backprobe the START circuit at the ignition switch harness and at the control module harness. Verify voltage is low/near 0 V when key is OFF/ON (not cranking).
  5. Turn key to START and observe the START circuit voltage; it should show battery voltage only while cranking. If voltage is high when it should be low, suspect short or switch fault.
  6. If circuit is high when key is OFF, disconnect the ignition switch connector: if voltage drops at the module side, the switch or its internal wiring is likely at fault; if voltage remains high at the module side, suspect wiring short to battery or module fault.
  7. Check continuity between START circuit and battery; wiggle harness to try to reproduce fault. Isolate any sections showing a short to battery.
  8. Inspect/remove any aftermarket devices tied into the START circuit (immobilizer, remote start) and test again.
  9. If wiring and external components check good, perform module input circuit testing per manufacturer procedure (resistance/voltage checks) and consider ECU/BCM replacement only after confirming upstream wiring and switch faults are not present.
  10. After repairs, clear codes and perform several start cycles and a road/usage cycle to confirm code does not return.

Likely causes

  • Ignition switch mechanical/electrical failure
  • Wiring short to constant battery voltage on START wire
  • Corrosion or loose connector at the ignition switch harness
  • Aftermarket device wiring connected to START feed

Fault status

⚠️ Status
Ignition switch START position circuit - voltage high (START input detected as high when not expected).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B2100 B2101 B2103 P0651
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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