B3660

Code

Generic B — Body

Occupant Classification System (OCS) Sensor Fault

Brand: Generic

Type: B — Body

Views: UK: 24 EN: 30 RU: 22

AI status

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Page language: EN

Causes

Open or short in OCS sensor wiring or connector
Corroded or disconnected seat harness connector (under-seat)
Failed occupant classification sensor (seat cushion module)
Water/moisture intrusion into the seat cushion or sensor
Faulty SRS/airbag control module or software error
Physical damage to seat cushion, sensor mat, or seat frame mounting

Symptoms

Airbag warning light (SRS) illuminated on dash
Passenger airbag status message shows 'OFF' or 'SERVICE' for passenger restraint
Passenger presence/weight detection incorrect or inconsistent
DTC B3660 stored in SRS control module (may be accompanied by other SRS codes)
Intermittent or permanent loss of passenger-side airbag functionality

What to check

Read and record SRS codes and freeze frame data with a capable scan tool
Visually inspect passenger seat upholstery and cushion for tears, moisture, or damage
Inspect under‑seat connectors and wiring for corrosion, loose pins, bent terminals, or chafing
Perform a wiggle test on the seat harness and observe scan tool for code change or signal dropouts
Check for water or debris in seat cushion seams and under the seat
Confirm recent service or collision history that may have affected seat wiring or connectors

Signal parameters

Sensor power/reference: typically vehicle reference voltage (check manufacturer spec; often ~5V)
Sensor ground: near 0V (verify continuity to chassis/ECU ground)
Signal output: varies with occupant load — compare live voltage or CAN message to manufacturer data
Resistance/continuity: measure between sensor mat terminals and compare with factory spec
CAN or LIN messaging (if used): verify presence of expected message IDs and update rate with scan tool

Diagnostic algorithm

Safety first: follow the vehicle manufacturer’s SRS service procedures before working on the system (disable battery and observe recommended wait times).
Connect a scan tool that supports SRS and record all stored codes, freeze frame, and live data from the occupant classification sensor.
Inspect the passenger seat for visible damage, moisture, or foreign objects. Remove seat trim as needed to access the sensor mat and connector.
Visually inspect and, if necessary, disconnect the under‑seat connector. Check pins for corrosion, bending, or pushed‑out terminals. Reconnect securely and recheck codes.
With the scan tool monitoring live data, perform a wiggle/test of the seat harness and connectors while watching for changes or intermittent faults.
Measure reference voltage and ground at the OCS connector; compare to manufacturer values. Measure the sensor output signal (or resistance across sensor mat elements) and compare to service data.
If wiring, power, or ground faults are found, repair wiring or connectors and retest. If wiring checks are good but sensor outputs are out of specification or intermittent, consider replacing the occupant classification sensor/seat cushion assembly.
After repairs, clear codes and perform the manufacturer-recommended SRS self-test or occupant detection calibration procedure. Verify that the airbag light extinguishes and the OCS behaves correctly under test loads.
If fault persists after replacement of sensor and wiring, consider SRS/airbag module diagnostics or ECU reprogramming per manufacturer guidance and refer to technical service bulletins.

Likely causes

Damaged or pinched wiring in seat harness (common at seat rails)
Connector contamination/corrosion at under-seat plug
Failure of the sensor mat inside the passenger seat cushion
Water ingress from a spill or leak soaking the sensor mat
Intermittent contact caused by seat position or movement

Fault status

⚠️ Status

Occupant Classification System (OCS) Sensor Fault — fault detected in passenger seat occupancy sensing circuit. SRS/airbag system may be disabled or degraded; service required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours