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Home / DTC / B1BA6 — Occupant class undetermined

B1BA6 — Occupant class undetermined

Detailed page for trouble code B1BA6.

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B1BA6

MITSUBISHI B — Body

Occupant class undetermined

Brand: MITSUBISHI
Type: B — Body
Views: UK: 18 EN: 38 RU: 23
AI status
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ready
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Page language: EN

Causes

  • Faulty occupant detection sensor/mat (pressure/weight sensor) under the seat
  • Damaged or disconnected wiring harness or connector under the seat
  • Corroded or pushed-out connector pins, water ingress, or physical damage to seat wiring
  • Faulty seat belt buckle switch or seat position sensor affecting classification logic
  • Intermittent or missing reference power, ground, or signal to the sensor
  • Software/calibration error in the airbag control module (requires recalibration or reflash)

Symptoms

  • SRS/Airbag warning lamp illuminated on dash
  • Passenger airbag status shows OFF, UNDETERMINED, or refuses to change state
  • Occupant classification indicator may show unknown or not-allowed messages
  • Possible inability to pass vehicle self-check or complete OCS calibration
  • Intermittent SRS light depending on seat movement or occupant presence

What to check

  • Read and record all SRS/OCS-related DTCs and freeze-frame data with a compatible scan tool
  • Clear codes and see if B1BA6 returns immediately or after seat movement/use
  • Visually inspect under the passenger seat: connectors, clips, harness routing, chafing, burnt/loose pins, water stains
  • Check for aftermarket seat covers, foam inserts, or repairs that could affect sensor mat
  • Inspect seat belt buckle switch and wiring for continuity and correct operation
  • Confirm correct power (ignition-switched 12 V), ground, and reference signal to the occupant sensor connector

Signal parameters

  • OCS reference supply (typically an internal reference ~5 V — verify against service manual)
  • Sensor output voltage: typically 0–5 V signal or pulsed/encoded data depending on system type (compare with factory values)
  • Resistance/continuity across seat mat terminals (service manual expected values)
  • Seat belt buckle switch: open/closed state (continuity) and expected voltage on buckleswitch circuit
  • Data-bus/ACM communication status (CAN/SWC frames relevant to SRS)
  • Ground integrity at sensor ground point (low milliohm expected)

Diagnostic algorithm

  1. Retrieve all SRS/OCS DTCs and freeze frame with a compatible scan tool; note any related codes. Do not assume B1BA6 is sole issue.
  2. Follow safe SRS procedures: disable battery per manufacturer, wait recommended time before working on airbag circuits.
  3. Visually inspect under passenger seat: connectors, clips, harness routing; look for physical damage, water/intrusion, aftermarket covers, or recent repairs.
  4. Reconnect battery and with scan tool monitor real-time OCS values while gently applying load to the seat mat; observe if sensor output changes or is stable/erratic.
  5. With ignition on, verify reference voltage, signal voltage, and ground at the occupant sensor connector; compare to service manual values.
  6. Check continuity and pin condition at all relevant connectors (seat harness to floor, occupant sensor connector, buckle switch connector). Repair corroded/bent pins or damaged wiring as needed.
  7. Test seat belt buckle switch for correct operation (open/closed) and associated wiring.
  8. If wiring and connectors are good but sensor output is out of range or inconsistent, remove seat cushion as required and measure resistance/continuity of the sensor mat per service data. Replace mat if out of spec or damaged.
  9. If sensor and wiring test good, verify ACM software/calibration status. Perform OCS recalibration or module reprogramming if required by service manual.
  10. If problem persists after replacing faulty components and completing calibration, consider ACM replacement — confirm with manufacturer diagnostic procedures before replacing.
  11. After repairs, clear codes, perform prescribed calibration, and verify the SRS light stays off during multiple ignition cycles and seat conditions.

Likely causes

  • Broken or shorted cable in seat harness under the seat
  • Connector pin corrosion or bent terminal at the OCS connector
  • Occupant sensor mat damaged by spillage or seat repair work
  • Seat back/position out of range or seat track damage affecting sensor readings
  • Recent battery disconnection, module replacement, or seat work without completing OCS calibration

Fault status

⚠️ Status
Occupant class undetermined — the OCS/airbag control module cannot classify the passenger seat occupant. Passenger airbag may be disabled or set to a default state; SRS warning lamp will be illuminated until the issue is resolved.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5 - 3.0 hours

Similar codes

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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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