B1A57

Code

Generic B — Body

Occupant Classification System Sensor Circuit Fault

Brand: Generic

Type: B — Body

Views: UK: 15 EN: 21 RU: 19

AI status

Completed

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Page language: EN

Causes

Open or short in occupant sensor harness or connector
Corroded, loose, or damaged seat connector pins
Faulty occupant classification sensor/mat/module
Water intrusion or contamination in the seat or connector
Damaged wiring from seat movement (rails, recliner, heater)
Faulty SRS/airbag control module or LIN/CAN communication error

Symptoms

SRS/airbag warning lamp illuminated on dash
Passenger airbag disabled or enabled incorrectly
Occupant detection incorrect or inconsistent (message or lamp)
Seatbelt reminder/indicator abnormal behavior
Diagnostic trouble code B1A57 stored in SRS module
Possible safety system messages on cluster or infotainment

What to check

Use an appropriate scan tool to read SRS codes, freeze frame and live data for occupant sensor values
Visually inspect seat, connectors, and wiring harness under seat and along seat tracks for chafing, pinched wiring, or corrosion
Check connector pins for corrosion, bent pins or water intrusion; reseat connectors
Perform wiggle test while monitoring live data for intermittent changes
Inspect seat cover/matting—remove aftermarket covers that may interfere with sensor
Check for related TSBs or calibration procedures

Signal parameters

OCS sensor output: typically analog voltage or resistive change reported to SRS module (manufacturer-specific)
Typical signal range: 0–5 V analog or variable resistance; some systems use LIN/CAN digital messages (refer to service manual)
Wake-up/power supply: 8–16 V depending on vehicle electrical system and module design
Expected resistance/continuity: varies by manufacturer—consult vehicle service data before replacing components
Communication: look for LIN/CAN traffic if the sensor is networked; no traffic may indicate module/communication fault

Diagnostic algorithm

Read and record all SRS codes, freeze-frame and live data for the occupant sensor. Note related codes.
Follow SRS safe work procedures (disable battery as required; wait manufacturer-specified time) before probing connectors.
Visually inspect seat cushion, sensor mat, connectors and harness routing; remove seat trim if needed to access sensor and connectors.
With connectors exposed, inspect pins for corrosion, damage or back-pinned terminals. Clean and reseat connectors; repair damaged pins or terminals.
Reconnect battery (if removed) and use a scan tool to monitor occupant sensor live data while performing a gentle wiggle test of harness, seat tracks, and connectors to detect intermittent faults.
Measure supply voltage, ground continuity, and sensor output per service manual. Check for open/short to ground or battery. If values are outside expected range, trace and repair wiring harness.
If wiring and connectors are good, test or measure the sensor mat resistance/output per factory procedure. Replace the occupant sensor/mat if out of specification or physically damaged.
If sensor and wiring check good, verify SRS control module operation and LIN/CAN communication. Reprogram or replace module if it fails diagnostics and all other causes eliminated.
After repairs, clear DTCs and perform required occupant sensor calibration or automatic relearn per manufacturer. Confirm fault does not return and verify correct passenger airbag status.
If intermittent or unresolved, consider swapping with a known-good module/sensor (where possible) and consult OEM service information or updated software/TSBs.

Likely causes

Open/short in sensor circuit or connector (most common)
Corrosion/moisture in seat harness connector
Damaged sensor mat from impact or wear
Faulty occupant classification module
Faulty/incorrectly configured SRS control module or software

Fault status

⚠️ Status

Occupant Classification System Sensor Circuit Fault — electrical or data fault in passenger seat occupancy sensor circuit; may cause passenger airbag enable/disable errors.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours