B1B3B

Code

Generic B — Body

Occupant Classification Module Configuration Mismatch (SRS)

Brand: Generic

Type: B — Body

Views: UK: 16 EN: 25 RU: 18

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Replacement OCM fitted with incorrect part number or software version
Incorrect module coding or calibration data
Corrupted or lost OCM configuration after battery disconnect or software update
CAN/LIN communication errors between OCM and other SRS modules
Physical damage or water intrusion in the seat/OCM connector or sensor mat

Symptoms

SRS / airbag warning lamp illuminated on dash
Passenger airbag status/message incorrect (e.g., 'airbag off' when occupied) or disabled
Occupant detection (seat-belt reminder or passenger occupancy) not working correctly
Fault stored in SRS control module with code B1B3B
Potential failure of related restraints until fault is cleared and issue resolved

What to check

Read SRS system with a capable scan tool; record all SRS-related DTCs and freeze frame data
Confirm vehicle battery voltage is stable (>12V) during diagnostics
Compare OCM part number, hardware and software (firmware) ID to factory specification
Check module coding/calibration values and VIN linkage in OCM and SRS master module
Inspect seat connector(s), OCM connector, and wiring for corrosion, bent pins, or water ingress
Check continuity/resistance of occupant classification mat sensor circuits per service manual

Signal parameters

OCM supply voltage: ~12 V (nominal when vehicle on)
Module ground resistance: low (
Occupant mat sensor resistance or pixel counts per manufacturer service data
CAN bus: OCM transmits/receives designated message IDs; no bus errors or timeouts
Module software/hardware ID string and coding bytes visible via scan tool

Diagnostic algorithm

Connect a diagnostic scanner with SRS capability. Read and record all SRS codes and module info (hardware/software versions, coding).
Verify battery voltage is adequate and stable. Recharge if needed before proceeding.
Inspect physical condition of passenger seat, occupant classification mat, seat wiring harness, and connectors for corrosion, damage, or water ingress. Repair any wiring issues and re-check codes.
Confirm the OCM part number and software match the vehicle's required configuration (compare to OEM reference). If a replacement OCM is fitted, verify it was programmed/coded to the vehicle VIN.
Use the scan tool to compare configuration/coding bytes between OCM and SRS master module. Correct any incorrect coding following manufacturer procedure.
Check CAN bus health: look for bus-off, high error counters, or missing OCM messages. Repair any bus wiring or termination faults.
If coding and wiring are correct, perform OCM calibration/occupant detection calibration per service procedure (some vehicles require a zeroing procedure after replacement).
If software mismatch is present, update OCM firmware and/or SRS master module software as recommended by manufacturer and re-code as needed.
Clear codes, cycle ignition, and confirm the SRS lamp extinguishes and occupant detection functions correctly. If codes return, escalate to manufacturer technical support and consider module replacement following correct programming steps.
Document repair steps, replaced parts, and any programming performed.

Likely causes

OCM replaced but not coded/programmed to vehicle VIN or trim (most common)
Software/firmware mismatch between OCM and SRS master module after update
Faulty or poor connector pins at OCM or seat harness
Damaged occupant classification sensor mat (resistive sensor or sensor cluster)
Intermittent CAN bus voltage or ground problem affecting module recognition

Fault status

⚠️ Status

Occupant Classification Module configuration mismatch detected. Verify module part number, coding and software; check connectors, wiring and occupant sensor mat. SRS warning lamp likely illuminated and passenger airbag/occupant detection may be disabled until resolved.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours