B179A

Code

Generic B — Body

Occupant Classification Sensor Circuit Fault

Brand: Generic

Type: B — Body

Views: UK: 12 EN: 14 RU: 11

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Page language: EN

Causes

Broken, chafed or pinched wiring in the seat harness
Loose, corroded or damaged connector pins at the OCS or airbag ECU
Damaged or wet occupant classification sensor mat/module in the seat
Poor ground or low reference voltage to the sensor
Incorrect or damaged seat cover or aftermarket seat interfering with the sensor
Intermittent connection from seat movement or previous seat repairs

Symptoms

SRS/airbag warning light illuminated on dash
Front passenger airbag disabled or 'passenger airbag off' status incorrect
Stored DTC B179A (and possibly other SRS related codes)
Intermittent SRS light associated with seat movement or passenger seating

What to check

Read and record all SRS codes and freeze frame data with a capable scan tool
Inspect seat area for visible damage, spills, or aftermarket seat covers
Visually inspect connectors and pin condition at the OCS and SRS ECU
Check battery voltage and ensure charging system is healthy before diagnosis
Use live data to monitor OCS status/sensor outputs while someone sits in different positions (follow safety procedures)
Wiggle test wiring and connectors while observing live data or DTCs for intermittency

Signal parameters

Sensor modules typically use a stable reference voltage (commonly 5 V — varies by manufacturer); reference should be within manufacturer tolerance
Ground at sensor should read near 0 V with respect to battery ground (
Signal/output voltage varies with occupant detection (typically within 0–5 V or 0–3.3 V range depending on system); consult OEM specs for exact ranges
Some systems report occupant classification over a dedicated data line or CAN message; update rate and payload depend on vehicle

Diagnostic algorithm

Safety first: follow manufacturer procedure for SRS work — disable battery (disconnect negative terminal) and wait specified time before doing repairs near airbags.
Use a factory-capable scan tool to read all SRS codes and live data. Note any related codes (ECU communications, multiple seat sensors, power/ground faults).
Visually inspect the passenger seat, upholstery, and connectors for contamination, damage, or previous repair evidence. Pay attention to areas where harness passes through seat frame.
With battery connected and vehicle in a safe state per OEM guidance, monitor the OCS live data or relevant CAN messages while performing gentle wiggle tests on the seat harness and connectors to reproduce the fault.
Check sensor connector pins for corrosion, bent pins, or poor mating. Repair or replace connector as needed.
Measure reference voltage and ground at the sensor connector; compare to OEM tolerances. Repair wiring if reference or ground is out of range.
If accessible, measure sensor outputs (or resistance of sensor mat if specified by OEM). Verify output changes when the seat is loaded/unloaded per documented test procedure.
If wiring tests show open/short/intermittent, trace and repair the harness (repair, replace grommets, secure routing to prevent chafing).
If wiring and connectors are good but the sensor output is out of range or does not change with load, replace the occupant classification sensor/module and retest.
After repairs, clear codes and perform required occupant classification calibration or initialization procedures per manufacturer. Verify that the SRS lamp extinguishes and no codes return.
If fault persists after sensor and harness checks, consider SRS control module inspection or replacement and consult manufacturer service information or TSBs.