B3641

Code

Generic B — Body

Occupant Classification Sensor Circuit Fault

Brand: Generic

Type: B — Body

Views: UK: 18 EN: 14 RU: 17

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Page language: EN

Causes

Open, shorted or corroded wiring/connectors in occupant classification (OCS) harness
Damaged or failed occupant classification sensor/seat mat module
Water/moisture intrusion in seat or connector
Poor electrical ground or lost reference voltage
Faulty airbag/occupant classification control module (ECU)
Incorrect or damaged seat cover/aftermarket seat causing sensor interference

Symptoms

Airbag warning lamp illuminated and/or passenger airbag status indicator active
Passenger airbag may be disabled when seat is occupied or enabled when empty
Chime or message indicating passenger airbag fault
Intermittent faults that change with seat position or when someone sits
Possible stored DTCs related to passenger restraint/airbag system

What to check

Scan for all stored airbag/OCS DTCs and record freeze-frame data
Visual inspection of seat connectors, harness routing and any signs of water or damage
Check for bent pins, corrosion and secure connector mating at the seat and module
Confirm battery voltage and perform an electrical supply/ground check at the OCS module
Wiggle test connectors and seat wiring while monitoring live data for changes
Verify whether OCS calibration or relearn is required or recently performed

Signal parameters

Reference voltage to sensor typically ~5 V (varies by manufacturer) with ignition ON
Sensor return/signal voltage varies with occupancy; expect a change when weight applied (0–5 V range)
Resistance across some sensor pads may change with load (open circuit indicates broken sensor)
Short to battery (B+) or ground will show near 12 V or 0 V respectively on the signal line
CAN/serial messages may show OCS status if sensor communicates digitally

Diagnostic algorithm

Read and record all airbag and body module codes and freeze frame data with a capable scan tool.
Follow manufacturer safety procedure for SRS work (disable battery/airbag system if required) before accessing seat wiring.
Visually inspect the passenger seat upholstery, connectors beneath the seat, and wiring grommets for damage, moisture or foreign objects.
Reconnect and firmly seat all connectors. Check for corrosion or bent pins; clean or repair as needed.
With ignition ON, backprobe the sensor connector: verify reference voltage (~5 V), ground continuity and the signal line behavior when seat is occupied/unoccupied. Note any constant short to 0 V or 12 V.
If signal is open or intermittent, trace continuity of signal and ground wires from seat connector to the OCS module; repair any breaks or shorts.
If wiring and connectors are good, test or replace the occupant classification sensor module (seat pad). Some systems allow resistance or voltage checks across sensor elements—compare to spec if available.
If sensor replacement doesn’t clear the fault, test or replace the occupant classification/airbag control module per manufacturer guidance.
After repairs, clear DTCs and perform the required occupant classification system calibration/relearn procedure per service manual.
Confirm repairs by verifying no reoccurrence of B3641 and proper passenger airbag enable/disable behavior with different occupancy conditions.

Likely causes

Connector corrosion or bent pins at the seat harness
Broken or pinched signal wire inside seat structure
Failed sensor assembly in the passenger seat cushion
Moisture contamination of the sensor pad
Loss of the 5V reference or ground to the sensor from the airbag/OCS module

Fault status

⚠️ Status

Occupant Classification Sensor Circuit Fault — electrical fault detected in passenger seat occupancy sensor circuit; may disable or misreport passenger airbag status.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours