B29C5

Code

Generic B — Body

Airbag System: Occupant Classification Sensor Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 15 EN: 16 RU: 6

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Broken/open or shorted wiring between occupant classification sensor and SRS control unit
Corroded, loose or damaged connector at the seat sensor/module
Failed occupant classification sensor (seat pad module)
Faulty SRS control module or intermediate gateway module
Software/configuration mismatch or missing calibration after repair
Water intrusion or mechanical damage to seat sensor or harness

SRS/airbag warning lamp ON (steady)
Passenger airbag disable/enable indicator may be incorrect or not operate
Possible loss of passenger-side airbag decision logic (passenger airbag may be disabled)
Stored DTC(s) related to seat/occupant sensor communication
In some vehicles, seatbelt reminder or other safety subsystems may show faults

Connect a capable OBD scan tool; read DTCs and freeze-frame data
Check for additional SRS and network (U-code) faults that indicate bus problems
Visually inspect seat area, covers and connectors for moisture, damage or loose clips
With ignition ON (follow OEM SRS safety procedures), verify sensor connector pins for bent/corroded terminals
Check for proper power and ground at the sensor connector per factory data
Perform wiggle test of seat wiring while observing live data/communication status

Sensor supply voltage — typically 5 V reference (verify with OEM spec)
Ground continuity between sensor and vehicle chassis ground
Signal/communication: CAN bus idle ~2.5 V per line (differential communication) or LIN/serial per OEM (verify protocol)
Expected presence of periodic CAN/LIN messages from occupant sensor when ignition ON
Open/short to battery or ground will show 0 V or battery voltage on signal lines (consult factory values)
Typical communication error codes/timeouts as reported by SRS module (see service manual)

Safety first: follow manufacturer SRS procedures (disable SRS power if required) before servicing seat or connectors
Read and record all stored DTCs and freeze-frame data with a bidirectional scan tool. Note if fault is permanent or pending.
Clear codes and attempt to reproduce. If B29C5 returns, continue diagnostics.
Visually inspect seat, occupant-sensor area, connector(s) and harness routing for physical damage or contamination.
With connector disconnected, inspect terminals for corrosion, deformation or contamination. Repair or replace connector as needed.
With ignition ON and using appropriate safety procedures, verify supply voltage and ground at the sensor connector against OEM values.
Check communication lines (CAN/LIN) for correct idle voltage and signals using a multimeter or oscilloscope. Look for missing messages or noise.
Perform continuity/resistance checks between the sensor connector and SRS module; repair any open/short circuits.
If wiring and connectors test good, attempt substitution with a known-good occupant classification sensor or module if available.
Check for required software updates or calibrations; perform sensor/seat calibration per factory procedure after replacement/repair.
After repair, clear codes, re-enable SRS, and verify normal operation and that the SRS warning lamp stays off.
If at any point airbag system repairs are performed, follow all safety and disposal rules for pyrotechnic devices and modules.