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Home / DTC / B1A0A — KOS key3 performance

B1A0A — KOS key3 performance

Detailed page for trouble code B1A0A.

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B1A0A

MITSUBISHI B — Body

KOS key3 performance

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

Causes

  • Weak or dead key fob/transponder battery
  • Damaged or mis-programmed key/transponder
  • Faulty KOS antenna/reader (start button or receiver module)
  • Wiring fault (power, ground, signal) to KOS module or antenna
  • Interference or poor RF coupling between key and vehicle
  • Faulty KOS/immobilizer ECU or software error

Symptoms

  • Intermittent or failed recognition of one key (key3)
  • Vehicle refuses to start or immobilizer warning lamp illuminates
  • Start/stop button requires close contact or specific position to start
  • Warning message about key or check key fob displayed
  • Inconsistent behavior between different keys (one works, one doesn't)

What to check

  • Read freeze frame data and related codes with a scan tool
  • Verify which key(s) fail by testing all known keys (spare keys)
  • Check key fob battery voltage
  • Inspect antenna/reader and connector at start button and KOS module
  • Measure supply voltage and ground at KOS module and antenna
  • Check for corrosion, bent pins, or damaged wiring in harness

Signal parameters

  • Key RF field strength (dBm) or RSSI read by receiver
  • Transponder ID and match status
  • Key response timing / handshake latency
  • Module supply voltage (V) and ground integrity
  • CAN/LIN message presence, frequency and error counters
  • Antenna impedance / continuity (ohms) where applicable

Diagnostic algorithm

  1. Retrieve DTC and freeze frame with manufacturer-grade scan tool; record related codes and timestamp.
  2. Confirm which physical key (key3) is reported. Test operation with that key and a known-good spare key to establish symptom consistency.
  3. Check and, if low, replace the key fob/transponder battery. Re-test key recognition.
  4. Visually inspect antenna/reader, connectors and wiring at the start button and KOS module. Repair any damaged wiring or corroded connectors.
  5. Measure supply voltage and ground at the KOS module and antenna during attempted recognition. Repair low supply or poor ground conditions.
  6. Use a diagnostic tool or RF tester (if available) to verify RF signal strength/reception from the key at the vehicle. Move key around start area to check for dead zones.
  7. Check for and clear related communications codes (CAN/LIN). If communication faults exist, diagnose the network wiring and nodes per network diagnostics.
  8. If the key fails but spare works, reprogram or relearn key3 per manufacturer procedure; if reprogramming fails, suspect the key or KOS module.
  9. If tests point to a faulty antenna/reader or KOS module, replace the defective component and perform required registration/relearn procedures.
  10. After repair, clear codes and verify repeatability of the fault-free operation with all keys; road/test as needed.

Likely causes

  • Key fob battery low for the specific key (key3)
  • Antenna or reader near the start button faulty or misaligned
  • Poor ground or low supply voltage to KOS module
  • Corroded connector or damaged coax/wiring to antenna
  • Key encoding or transponder ID not learned or corrupted
  • Intermittent wiring or connector connection in harness

Fault status

⚠️ Status
KOS key3 performance — key recognition/performance out of range. Check key, antenna, wiring, and KOS module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

B1A0B B1A0C B2797 U0073 P1620
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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