B18C3

Code

Generic B — Body

Occupant Detection System: Rear Center Seat Sensor Fault

Brand: Generic

Type: B — Body

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AI status

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Page language: EN

Causes

Open, short or high-resistance wiring between rear center seat sensor and SRS/occupant module
Corroded, loose or contaminated connector at the seat sensor
Damaged or torn seat sensor mat (pressure/resistive or capacitive)
Water/moisture intrusion in seat or connector
Improperly seated or pinched harness after seat removal or repair
Faulty occupant detection module or SRS module input circuit

Symptoms

Rear center seat occupant indicator shows incorrect status (occupied/unoccupied)
Seatbelt reminder/chime may activate incorrectly for rear center seat
Airbag/seat suppression function for rear center seat may be disabled or unavailable
SRS/airbag warning or occupant detection warning lamp may illuminate
DTC B18C3 stored in SRS/occupant detection module
Intermittent or no signal changes when weight is applied to rear center seat

What to check

Use a capable scan tool to read B18C3 and any related SRS/occupant detection codes; record freeze frame and live data
Visually inspect rear center seat, seat cover, and underside for liquid damage, tears, or foreign objects
Inspect and reseat connectors for the rear center seat sensor; check for corrosion, bent pins, or water intrusion
Perform a wiggle test: monitor live data while moving seat cushion and harness to look for intermittent changes
Measure continuity and resistance across the sensor mat circuit per manufacturer procedure (compare to spec)
Check for proper reference voltage and ground at the sensor connector with ignition ON (verify against factory data)

Signal parameters

Reference voltage at sensor connector: typically ~5 V (verify with factory data before assuming)
Signal output: variable voltage or switched/logic level to occupant module (0–5 V range commonly used); may present as binary occupied/unoccupied in live data
Sensor mat resistance: varies by design — an open/infinite or shorted reading indicates a failed mat (check with factory specs)
Live-data response: applying weight to seat should change the occupant sensor status and signal reading in scan tool
If capacitive sensor used: watch for stable baseline and measurable change when an occupant sits (no sudden erratic spikes)

Diagnostic algorithm

Connect scan tool, retrieve B18C3 and any other stored SRS/occupant codes; note freeze frame and live parameters for the rear center seat input.
Inspect seat surface and underside for visible damage, liquid stains, or signs of repair. Check for objects that may interfere with the mat.
With battery connected and ignition ON (as required by OEM), visually inspect and disconnect the rear center seat sensor connector; check pins for corrosion, damage, or pushed-out terminals.
Backprobe the sensor connector and verify reference voltage and ground (compare to factory values). If no reference, trace and repair power/ground supply to module.
Measure resistance/continuity of the seat sensor mat (with connector disconnected) and compare to specification; an open or out-of-range value suggests a faulty mat.
Perform a wiggle test on the harness and connector while monitoring live data to find intermittent faults. Repair any broken wires or poor crimps.
If wiring and connector check good, replace the seat sensor mat/module with a known good unit or attempt sensor repair per OEM guidance.
After repair or replacement, clear DTCs and perform the required occupant sensor calibration procedure using the scan tool or OEM calibration routine.
Verify proper operation: confirm live-data changes with weight on the seat, confirm no return of B18C3 after test/road cycle, and ensure SRS/occupant indicators behave correctly.
If fault persists after sensor and wiring verified, consider diagnostic on SRS/occupant detection control module input circuitry or update module software per manufacturer.

Likely causes

Connector pins pushed out, bent, or corroded at rear center seat harness
Seat cushion removal or reinstallation pinched the sensor cable
Seat mat wiring worn through by body/seat movement
Infiltration of liquid into seat cushion area causing sensor failure
Sensor mat delamination or internal element break
Grounding point for the seat sensor circuit loose or corroded

Fault status

⚠️ Status

Occupant Detection System — Rear Center Seat Sensor Fault. The rear center seat sensor signal is out of expected range or not detected. Occupant detection/airbag suppression for this seat may be unavailable until fault is corrected and system is calibrated.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours