B18C0

Code

Generic B — Body

Front Passenger Occupant Classification Sensor Circuit Fault

Brand: Generic

Type: B — Body

Views: UK: 10 EN: 16 RU: 17

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Page language: EN

Causes

Open, shorted or corroded wiring in the passenger seat sensor harness
Poor or contaminated connector pins at the occupant classification sensor or airbag/OCS module
Failed occupant classification sensor (sensor mat or module in the seat)
Water or debris intrusion into the seat cushion or sensor connector
Faulty airbag/occupant classification control module or software fault
Recent seat repair/replacement or improper reinstallation (improper connector seating, damaged clips)

Symptoms

Airbag warning lamp illuminated
Passenger airbag status indicator may read OFF when occupied, or fail to change
Passenger airbag disabled or unpredictable deployment logic
DTC B18C0 (and possibly other OCS/airbag codes) stored in SRS module
Intermittent behavior relating to seat occupancy detection

What to check

Read and record DTCs and freeze-frame data with a capable scan tool
Visual inspection of passenger seat underside, connectors and harness routing
Check for corrosion, bent pins, water intrusion or damaged insulation at connectors
Backprobe sensor connector and check supply voltage and ground with ignition ON
Perform wiggle test of wiring and connectors while watching live data for changes
Measure resistance/continuity between sensor connector and airbag/OCS module (with battery disconnected where required by manufacturer SRS procedures)

Signal parameters

Supply voltage to sensor (key ON): approx. 11–14 V (system dependent)
Reference/ground: very low resistance to chassis ground (
Sensor output: typically an analog voltage or sensor bus signal (varies by manufacturer) — expect a stable voltage that changes with applied load; nominal ranges often 0.5–4.5 V for analog types
Continuity: no opens in the harness between sensor connector and module; wiring resistance should be low and stable
CAN/LIN comms (if used): module should appear on vehicle bus and respond to scan tool

Diagnostic algorithm

Safety first: follow SRS precautions. Disable battery per vehicle manufacturer instructions before disconnecting any airbag/occupant sensor connectors. Wait required time for system capacitors to discharge.
Use a scan tool to read and log all stored airbag and occupant classification codes and freeze-frame data. Note whether code is current or historical and any related codes.
Visually inspect the passenger seat area: underside of seat cushion, sensor mat connector, seat track area and wiring routing for damage, water, or contamination.
Reconnect battery (if disconnected for safety steps required for measurements) and backprobe the sensor connector with ignition ON (do not deploy SRS). Verify supply voltage, ground, and sensor output vs. expected ranges listed by manufacturer or general values above.
Perform a wiggle test on the seat wiring, connectors and harness while watching live data and DTC status. If fault toggles, isolate the area of movement and repair wiring/connectors.
With battery off, measure continuity and insulation resistance between sensor pins and the airbag module connector to check for opens or shorts. Repair any harness damage found.
If wiring and connectors are good, swap or bench-test the occupant classification sensor (if a known-good assembly is available) or replace the sensor mat assembly per service procedures.
If sensor replacement performed, follow manufacturer procedures for occupant classification system recalibration/zeroing and/or perform required occupant weight calibration with a scan tool.
Clear codes and perform a full system check. Verify proper passenger airbag status indications and confirm no return of B18C0 after road test or repeated seat movement tests.
If code persists and wiring and sensor are verified good, consult manufacturer technical service information for module-level faults or replace the occupant classification/airbag control module as directed.

Likely causes

Damaged or disconnected sensor connector under the passenger seat
Open or short in harness where it passes through seat frame or under carpet
Failed occupant classification sensor mat assembly
Corrosion or moisture in the connector causing intermittent circuit
Module fault or corrupted occupant classification calibration

Fault status

⚠️ Status

Front passenger occupant classification sensor circuit fault detected. Passenger airbag logic may be disabled or unreliable; inspect seat sensor, wiring, connectors and module.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours