B2951
Occupant Classification Sensor Fault
Causes
- Damaged or corroded connector or wiring in the seat harness
- Open, short or high resistance in sensor mat circuits
- Faulty occupant classification sensor module or mat
- Poor ground or missing reference voltage to the sensor
- Water intrusion, contamination, or mechanical damage to the sensor mat
- Incorrect or lost sensor calibration (software/ECU issue)
Symptoms
- Airbag / SRS warning lamp illuminated
- Passenger airbag status message (airbag disabled/enabled incorrectly)
- Driver/passenger seat occupant detection incorrect or unavailable
- Diagnostic trouble code B2951 stored in SRS module
- Possible chimes or dashboard messages related to passenger airbag
What to check
- Use a scan tool to read all SRS codes and freeze-frame data
- Visually inspect passenger seat, upholstery, connectors and harness for damage or contamination
- Check for any Service Bulletins or calibration procedures for occupant classification
- Verify connector pin integrity and presence of locking tabs
- Measure reference voltage and ground at sensor connector with key ON (typically 5V reference and sensor ground)
- Perform wiggle test on seat harness while monitoring scan tool for code changes
Signal parameters
- Reference voltage typically ~5 V at the sensor supply pin (varies by manufacturer)
- Sensor ground should be near 0 V with low resistance to chassis ground
- Signal output varies with occupancy (often a voltage or CAN/serial data representing weight or sensor zone values)
- Open circuit (infinite resistance) or short to ground/power on sensor lines indicates a fault
- Scan tool may display raw weight/zone values (e.g., 0–255 counts or kilograms) — unexpected or frozen values indicate a problem
Diagnostic algorithm
- Connect a capable scan tool, record all stored SRS codes and freeze-frame data; note if other SRS or communication codes are present.
- Visually inspect the passenger seat area for signs of water, debris, or damage; remove seat cushion trim if necessary to access mat and connectors.
- Disconnect battery per manufacturer safety procedure before disconnecting any SRS connectors; then inspect and reseat the occupant sensor connector(s).
- With battery reconnected and ignition ON (follow safe SRS procedures), verify reference voltage and ground at the sensor connector pins. Compare to manufacturer spec.
- Measure continuity/resistance of sensor mat circuits and harness between connector and sensor module. Look for opens, high resistance, or intermittent connections (wiggle test).
- If the wiring and connectors test good, use the scan tool to view live occupant sensor values or run the sensor self-test. Attempt a recalibration/initialization if procedure is available.
- If sensor outputs are out of range or calibration fails, replace the occupant classification mat/module or repair the identified damaged wiring/connector.
- After repair or replacement, clear codes, perform required calibration/initialization, and verify that the SRS light stays off and that occupant detection behaves correctly.
- If fault persists and wiring/sensor are good, investigate SRS control module functionality and inter-module communications (CAN/UART) as a potential cause.
Likely causes
- Connector pin corrosion or disconnected seat harness connector
- Broken wire in seat harness (pinched at seat frame or recliner)
- Failed sensor mat under seat cushion
- Loss of 5V reference or ground to the sensor
- Contamination (liquid, debris) causing mat short or open
Fault status
Similar codes
Available brands with manuals
AUDI 7
Audi A3 (1997) – 1.6L 4-cylinder (2‑valve) Engine Mechanical Components Service Manual (AEH, AKL, APF) – Edition 07.2002
Workshop ManualService manual for Audi A3 (1997) 1.6L 4‑cylinder (2‑valve) engines (codes AEH, AKL, APF). Includes technical data, engine removal/installation, crankshaft group, cylinder head and valve gear, lubrication, cooling and exhaust system procedures. Edition 07.2002.
AUDI A3 (2004) Workshop Manual — 2.0L FSI Turbo (4‑cyl, 4‑valve) Engine, Mechanics — Edition 03.2017
Workshop ManualOfficial workshop manual for the Audi A3 2.0L FSI turbo engine (mechanics). Includes step‑by‑step removal/install procedures, technical data, tightening torques and diagnostic/repair instructions. Intended for professional garages and experienced technicians.
Audi A3 2004 — Electrical System (Workshop Manual, Edition 02.2018)
Workshop ManualWorkshop manual for the Audi A3 (2004) — Electrical system. Includes procedures for battery, starter, alternator, gauges, wipers, exterior/interior lighting and wiring. Edition 02.2018.
Audi A4 / A4 Cabriolet – 4.2 l V8 (5‑valve, timing chains) – Workshop Manual (Mechanics) – Edition 04.2007
Workshop ManualComprehensive workshop manual for Audi A4 (2001) and A4 Cabriolet (2003) with the 4.2 L V8, 5‑valve engine with timing chains (Engine IDs BBK/BHF). Includes step‑by‑step procedures for engine removal/installation, crankshaft and timing chain service, cylinder head/valve gear, lubrication, cooling and exhaust system repairs. Intended for professional technicians and service workshops.
Audi A4 / A4 Cabriolet — Auxiliary Heater Workshop Manual (Edition 08.2004)
Workshop ManualWorkshop Manual for Audi A4 and A4 Cabriolet — Auxiliary Heater (Edition 08.2004). Contains self-diagnosis procedures, fault tables, electrical and fuel system checks, final control tests, CO₂ exhaust adjustment and step-by-step removal/installation and repair procedures. Intended for professional workshop use.
Audi A4 / A4 Cabriolet (1.8T 4‑cyl turbo) — Motronic Injection & Ignition System Service Manual (Edition 01.2015)
Workshop ManualService manual for Audi A4 (2001‑) and A4 Cabriolet (2003‑) with 1.8L 4‑cylinder turbo engines. Covers Motronic fuel injection and ignition systems, diagnostic and maintenance procedures. Includes technical data, removal/installation steps and system checks.
Audi Servicing Manual — 7‑Speed Dual Clutch Transmission 0CJ / 0CL / 0CK / 0DN / 0DP / 0HL (Edition 05.2018)
Workshop ManualService manual for the 7‑Speed dual‑clutch (DSG) transmissions 0CJ/0CL/0CK/0DN/0DP/0HL fitted to various Audi models. Includes repair information, clutch and gearbox disassembly/assembly, mechatronic and hydraulic system procedures, seals and differential work. Edition 05.2018.
LAND ROVER 2
Land Rover Defender 300Tdi — Workshop Manual (1996 model year)
Workshop ManualOfficial workshop manual for the Land Rover Defender 300Tdi (from 1996 model year). Contains specifications, adjustment, fault diagnosis and step-by-step repair and overhaul procedures for engine, transmission, axles, suspension, brakes, electrical and body. Intended for dealer workshops and trained technicians.
Land Rover Defender Workshop Manual Supplement & Body Repair Manual (1999 & 2002 MY)
Workshop ManualWorkshop Manual Supplement and Body Repair Manual for the Land Rover Defender. Includes general specifications, maintenance schedules, tuning data and step‑by‑step repair procedures for engine, transmission, suspension, brakes, electrical and body repairs. Covers Defender models from 1999 and 2002 model years.