B1A4B

Code

Generic B — Body

Occupant Classification System Sensor Fault

Brand: Generic

Type: B — Body

Views: UK: 0 EN: 0 RU: 1

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Page language: EN

Causes

Open, shorted, damaged, or corroded wiring/connector in the seat/OCS circuit
Failed occupant classification sensor (pressure/load cell, pad sensor, or mat sensor)
Loose, bent, or pushed-out connector pins at seat module or SRS control unit
Faulty Occupant Classification Module (OCM) or SRS control module
Water/moisture intrusion into seat sensor or connector
Improper seat cushion/cover installation, foreign object under seat pad, or aftermarket seats

Symptoms

SRS/Airbag warning light illuminated
Passenger airbag disabled or incorrect passenger airbag enable message
'Passenger Occupant' or 'OCS' warning/message on the dash or center display
Seatbelt reminder/indicator behavior may change
Vehicle may record multiple occupant classification-related DTCs
Possible inability to complete OCS calibration or allow airbag enable

What to check

Connect a capable scan tool; read and record all SRS/occupant classification DTCs and freeze frame data
View live OCS data (seat sensor voltages, weight/occupancy values, passenger enable flag) while changing seat load
Visually inspect seat cushion, seatback, connectors, and harness for damage, moisture, or foreign objects
Check connector terminals for corrosion, bent pins, or poor contact; reseat connectors
Verify power supply (typically 5 V reference or battery feed), ground integrity, and signal continuity at the sensor and module
Perform resistance/continuity checks on wiring harness per service manual values

Signal parameters

Sensor supply/reference: typically regulated 5 V or vehicle-specific reference (verify with OEM data)
Sensor signal: saddle/pressure sensors usually produce a voltage proportional to load — often in the ~0.5–4.5 V range (approximate)
Weight/occupancy output: system-calculated kg or occupant classification states (empty, child, small adult, adult) — live-data should change predictably with applied weight
Resistance/impedance: load-cell or switch matrix may show changing ohm readings as weight is applied (consult service manual for expected ranges)
CAN/CAN-FD messages: occupant classification module often publishes passenger presence and airbag enable flags — verify correct message and data on the bus

Diagnostic algorithm

Safety first: follow SRS safety procedures. Disable the battery and wait the manufacturer-specified time before handling SRS components.
Scan and record: read all DTCs and freeze-frame data with a scan tool that supports OCS/SRS. Note when the code set and any related codes.
Reproduce & observe: with battery connected and scan tool attached, observe live OCS sensor values while an assistant sits slowly and shifts weight. Note any unstable, noisy, or out-of-range readings.
Visual inspection: remove seat trim as required and inspect sensor pad, cushion wiring, connectors, and harness routing for mechanical damage, corrosion, or contamination.
Connector/wiring checks: disconnect connectors and inspect pins. Wiggle test wiring while watching live data or DTC status to find intermittent faults. Repair damaged wiring or terminals.
Power/ground verification: verify reference supply and ground at the sensor connector with a multimeter; confirm proper voltages per service data.
Signal verification: measure sensor output with known weights or bench test per OEM procedure. Compare to expected ranges or live-data behavior.
Module/harness isolation: if wiring and sensor checks pass, trace to and test the occupant classification module and its connectors. Check continuity between sensor and module pins.
Replace suspect component: if a sensor or connector is confirmed faulty, replace only with manufacturer-approved parts. If replacing the OCM or SRS control unit, follow required programming/calibration.
Calibrate and confirm: after repair or replacement, perform occupant classification calibration/initialization per factory procedure, clear codes, and verify correct live-data and that the airbag enable state behaves correctly.
Final verification: road test as required and re-scan SRS system to confirm no return of DTCs.

Likely causes

Damaged connector or wiring between the seat sensor and SRS control module (most common)
Failed seat occupancy sensor (pad/load cell) or its electronics
Moisture or contamination in the seat cushion/connector causing intermittent signals
Loose connector at the SRS/OCM module or poor ground
Incorrect module calibration or incompatible replacement component