B13C7

Code

Generic B — Body

Seat Occupancy Sensor Circuit C7 Fault

Brand: Generic

Type: B — Body

Views: UK: 7 EN: 11 RU: 7

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Page language: EN

Causes

Damaged or disconnected seat occupancy sensor (pressure mat or load cell)
Broken, chafed, or pinched wiring in the seat harness
Corroded or loose connector under the seat
Short to ground or to battery on the C7 circuit
Faulty seat control / occupant classification module or airbag ECU
Water/moisture intrusion into the seat cushion or connector

Symptoms

Airbag/airbag warning lamp illuminated
Passenger airbag may be disabled or incorrectly enabled
Seatbelt reminder or chime behaves incorrectly for that seating position
Occupant classification displays incorrect occupant status or refuses calibration
DTC stored as current or intermittent; possible fail-to-start in some vehicles that require occupant sensing

What to check

Use a diagnostic scanner to read B13C7 and any related occupant classification/body/airbag codes; record freeze‑frame and DTC status (current/intermittent)
Visually inspect the affected seat: cushion, seams, and underside for moisture or physical damage
Inspect connectors under the seat for corrosion, bent pins, or loose latches; ensure connectors are fully seated
Wiggle the harness and connectors while monitoring the DTC/live data to reproduce an intermittent fault
Check for recent service, seat removal, or aftermarket seat covers that could disturb the sensor mat
Confirm vehicle battery voltage is stable during tests (many sensors use 5 V reference)

Signal parameters

Supply/reference: typically a 5 V reference (verify specific model spec)
Ground: chassis ground continuity expected at seat connector
Signal: seat occupancy sensors produce a resistance change or voltage variation corresponding to load; signal range is manufacturer-specific — expected to be a finite voltage within 0–5 V or a resistance within specified ohms when intact
Open-circuit: infinite resistance / no signal; short to ground: ~0 Ω; short to battery: near battery voltage
Live-data occupancy status (Boolean or multi-level) should change when applying known load to the cushion

Diagnostic algorithm

Verify DTC: connect full-function scan tool, read B13C7 and related codes, note whether code is current or historic and any freeze-frame data.
Attempt code erase: clear codes, re-start vehicle and re-check if code returns (helps identify intermittent).
Visual inspection: remove seat trim as required; inspect sensor mat, wiring, and connectors for damage or signs of moisture/corrosion.
Connector check: disconnect seat connector(s), inspect pins for corrosion/broken pins, clean and re-seat. Check for water or debris in terminals.
Power/ground check: with key ON, verify reference voltage (often 5 V) and ground at seat connector per service manual. Do not short circuits.
Signal continuity/resistance: with battery disconnected if required by manufacturer, measure continuity/resistance of C7 sensor circuit from connector to sensor and across sensor elements. Compare to service specs. Look for open or short circuits.
Wiggle/intermittent test: with scanner monitoring live data, have an assistant wiggle the seat harness, connectors, and move seat rails to try to reproduce fault. Note changes in live data or DTC status.
Isolate sensor: if multiple sensor zones exist, isolate or unplug individual sensor mats (per manual) to see if code changes, or swap with a known-good seat/mat if available.
Repair wiring/connector faults: repair chafed wires, replace damaged connectors, apply dielectric grease for corrosion-prone terminals, and replace the occupant sensor mat if damaged.
Relearn/calibrate: after repair or replacement, perform any required occupant classification/seat calibration procedures with scan tool per manufacturer instructions.
Final verification: clear codes, complete calibration, drive/operate vehicle through required conditions and confirm B13C7 does not return.

Likely causes

Open circuit in C7 sensor wiring (broken conductor, disconnected connector)
Shorted signal or power/ground on the C7 harness from wear or seat movement
Damaged seat occupancy mat (punctures, delamination, moisture damage) producing out-of-spec resistance/voltage
Corrosion at the seat-to-body connector causing intermittent contact
Faulty occupant classification module or failed sensor electronics

Fault status

⚠️ Status

Stored/Active — Occupant classification seat occupancy sensor circuit C7 out-of-range, open, short, or intermittent. The airbag/occupant detection ECU has disabled or flagged that input.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours