B1C72

Code

Generic B — Body

Occupant Classification System — Sensor Circuit Malfunction

Brand: Generic

Type: B — Body

Views: UK: 10 EN: 11 RU: 7

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Page language: EN

Causes

Open, shorted or intermittent wiring between seat sensor mat and airbag/OCS control module
Corroded, loose or damaged connector under the seat
Faulty occupant classification sensor mat (seat cushion sensor)
Faulty Occupant Classification Module or Airbag Control Module
Water intrusion or contamination in the seat cushion
Aftermarket seat covers or repairs altering sensor operation

Symptoms

SRS/Airbag warning lamp illuminated
Passenger airbag disabled or unexpected passenger airbag status message
Seat occupant indicator incorrect or not updating
Possible intermittent SRS lamp resets tied to seat position
DTC B1C72 stored in airbag/OCS module

What to check

Read and record airbag/OCS DTCs and freeze frame with a capable scan tool
Visually inspect connectors and wiring under the affected seat for damage, corrosion, or pins pushed out
Check for evidence of liquid contamination or seat repair
Verify seat rails and harness routing for pinch points or chafing where wires pass
Perform wiggle test while monitoring live OCS data to reproduce fault
Verify manufacturer SRS service procedure and safe battery disconnect before doing continuity or resistance checks

Signal parameters

Sensor circuit typically has a reference supply (often ~5 V) and a variable signal that changes with applied weight
Expected signal: varies smoothly with occupant weight; sudden 0 V or battery voltage indicates short to ground or battery
Open-circuit/infinite resistance or erratic/noisy voltage indicates sensor or harness open/intermittent
Short to ground → signal near 0 V; short to battery → signal near battery voltage (~12 V)
Exact voltages/resistances and thresholds are manufacturer-specific — consult service data for values

Diagnostic algorithm

Retrieve and record all SRS/OCS fault codes and freeze-frame data with a qualified scan tool.
Confirm B1C72 is current and note whether related OCS or airbag codes are present.
Follow vehicle manufacturer SRS safety procedure (disable battery and wait recommended time) before accessing connectors.
Visually inspect seat cushion, sensor mat area, connectors and wiring for damage, contamination, or loose pins.
Reconnect any loose connectors; clean corroded contacts with appropriate electrical cleaner and reseat.
With power re-applied and using a scan tool, monitor the OCS live data while gently moving the seat and performing a wiggle test on the harness to try to reproduce the fault.
Measure reference voltage and signal voltage at the seat sensor connector while comparing to manufacturer values; check for short to ground or battery and for open circuit.
Perform continuity checks from the seat sensor connector back to the airbag/OCS module to identify opens or high resistance.
If the sensor mat shows out-of-spec signals or is contaminated/damaged, replace the sensor mat assembly per manufacturer instructions.
If wiring and sensors check good, consider module fault — verify connectors at module and replace module only after confirming all wiring/sensors are good.
Clear codes and perform a functional verification and road/seat-test to ensure the fault does not return.
Note: Always follow the vehicle manufacturer’s SRS handling and replacement procedures to avoid accidental deployment or injury.

Likely causes

Broken wire or chafed harness under seat causing intermittent contact
Connector pin corrosion or bent pins at sensor-to-harness plug
Sensor mat layer delaminated or internal trace failure from impact/wear
Control module detecting voltage out-of-range (open circuit or short to ground/power)
Sensor mat contamination from liquid spill or dampness

Fault status

⚠️ Status

Occupant Classification System sensor circuit malfunction detected (open/short/intermittent). The airbag control module cannot reliably read the seat occupancy sensor signal; passenger airbag status may be disabled and SRS warning lamp will be illuminated.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours