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Home / DTC / B2A20 — Passenger Occupant Classification System Fault

B2A20 — Passenger Occupant Classification System Fault

Detailed page for trouble code B2A20.

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B2A20

Generic B — Body

Passenger Occupant Classification System Fault

Brand: Generic
Type: B — Body
Views: UK: 0 EN: 2 RU: 0
AI status
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Page language: EN

Causes

  • Damaged or corroded connector(s) under passenger seat
  • Faulty occupant classification mat (pressure/weight sensor) or sensors
  • Open/short in wiring harness (seat to OCS/module)
  • Faulty Occupant Classification Module / SRS control unit
  • Failed seatbelt buckle/pretensioner sensor affecting classification input
  • Improper calibration or software error after seat/component replacement

Symptoms

  • SRS/Airbag warning lamp illuminated
  • Message indicating passenger airbag disabled or system fault on dash or center display
  • Passenger presence indicator incorrect (airbag off when seat occupied or vice versa)
  • Seatbelt reminder may not behave as expected
  • DTC B2A20 stored in SRS/OCS module memory

What to check

  • Read all stored SRS/OCS codes and freeze-frame data with an OBD-II/SRS-capable scan tool
  • Inspect battery voltage and chassis grounds; ensure stable power supply before testing
  • Visually inspect connectors and wiring under the passenger seat for damage, corrosion, water, or foreign objects
  • Check for related crash-data or airbag deployment history that may have permanently disabled circuits
  • Verify there are no additional SRS codes that point to module or bus communication faults
  • Perform a wiggle test on seat wiring while monitoring live data to see intermittent faults

Signal parameters

  • OCS supplies typically use vehicle battery (nominal 9–14 V) for power circuits — measure at connector pins per service manual
  • Occupant sensor output commonly appears as an analog voltage or resistance that changes with weight/pressure (monitor live sensor value with scan tool)
  • Some systems report occupancy as CAN/BUS messages or status bits — confirm expected occupancy state transitions (empty, child, adult) via scan tool
  • Seatbelt buckle switch should show stable closed/open continuity (0 Ω or OL) when operated; verify against service manual ranges
  • Expected signal stability: sensor outputs should be steady when static; large noise or intermittent spikes indicate wiring/sensor issue

Diagnostic algorithm

  1. Safety first: disable SRS power (disconnect battery and wait manufacturer-specified time) before accessing connectors or components under the seat
  2. Retrieve and record all SRS/OCS codes and freeze-frame data with an appropriate scan tool
  3. Visually inspect passenger seat area for contamination, fluids, or foreign objects and remove if present
  4. Reconnect battery, clear codes, and perform a live-data check while sitting in seat (or using a calibrated test tool) to observe occupant sensor responses
  5. With scan tool monitoring OCS values, perform a wiggle test along harness and connectors under the seat to check for intermittent changes or faults
  6. Measure power and ground at the OCS/module connectors; repair poor power/ground connections before further testing
  7. If available, measure seat mat sensor resistance/voltage at the sensor connector and compare to service manual; replace mat if out of range or erratic
  8. Check and verify seatbelt buckle switch and associated wiring as it can affect classification input
  9. If wiring and sensors test good, verify module communications (CAN/BUS) and perform module self-tests; reflashing or module replacement may be required if module fails diagnostics
  10. After repairs, perform required occupant classification calibration procedure with proper tools and following manufacturer instructions, then confirm no DTCs reappear

Likely causes

  • Connector wiring damage under seat (pinched, corroded, or loose)
  • Occupant classification mat failure (age, moisture, or mechanical damage)
  • Faulty Occupant Classification Module or SRS control unit
  • Required recalibration after seat replacement or repair

Fault status

⚠️ Status
Passenger Occupant Classification System fault detected. Passenger airbag/OCS may be disabled or operating incorrectly — inspect OCS wiring, sensors, and module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

B2A21 B2A22 B1620 B0100 B1651
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