B0166

Code

Generic B — Body

Passenger occupant classification sensor circuit malfunction

Brand: Generic

Type: B — Body

Views: UK: 11 EN: 8 RU: 4

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Page language: EN

Causes

Damaged or shorted wiring harness under passenger seat (open, short to ground or power)
Loose, corroded or disconnected connector at the occupant classification sensor or control module
Faulty occupant classification sensor mat (seat cushion sensor) or sensor module
Water ingress or contamination in the seat cushion or connectors
Improper seat cover or seat modifications interfering with sensors
Faulty SRS/airbag control module or software fault

Symptoms

SRS/airbag warning lamp illuminated on instrument panel
Message or indicator showing passenger airbag OFF or "service occupant classification system"
Passenger occupancy not detected or incorrectly classified (display may show "Passenger Off" when occupied)
Intermittent fault or occasional changes in passenger airbag status with seat movement or when someone sits down

What to check

Read and record DTCs and freeze frame data with an SRS-capable scan tool; note any related airbag codes
Visually inspect seat cushion, sensor mat and harness routing under the passenger seat for damage, water, contamination and pinched wires
Inspect connectors for corrosion, bent pins, poor crimps or disconnected terminals at the sensor mat and SRS module
With ignition on, monitor live data for occupant classification sensor signals and watch for changes when weight is applied or seat is moved
Perform a wiggle test on the harness and connectors while monitoring live data to try to reproduce the fault
Check for aftermarket seat covers or repairs that could affect mat sensors

Signal parameters

Reference voltage: typically 5.0 V (±0.5 V) at the sensor reference pin (verify with OEM data)
Signal voltage per sensor element: 0–5 V depending on load/occupancy (exact expected values depend on module design)
Sensor mat continuity: individual sensor elements should show continuity; open circuits indicate a failed element (refer to service manual for expected resistance ranges)
Ground continuity: low resistance to vehicle chassis ground from the sensor ground pin
Diagnostic module data: occupancy status states (empty, child/infant, adult) should change appropriately when weight is applied

Diagnostic algorithm

Safety first: follow manufacturer SRS precautions. Disconnect battery and wait the specified time before disconnecting airbag/occupant sensor connectors.
Use an SRS-capable scan tool to read codes, live data, and any DTC history. Note relevant PIDs or occupancy status messages.
Visually inspect the passenger seat area: seat cushion, underside, mat, connectors and harness routing for damage, water ingress, corrosion, or poor repairs.
Reconnect battery per safe procedure. With scan tool monitoring live data, perform a wiggle test of the harness and connectors under the seat while observing for signal changes or faults.
Measure reference voltage, signal voltage and ground at the occupant classification sensor connector (with harness connected if safe to do so). Compare to manufacturer specs. If no reference or poor ground, trace and repair wiring to source.
If wiring and connector integrity are confirmed, measure continuity or resistance of sensor mat elements per service manual. Replace the sensor mat if open or out-of-spec.
If sensor mat and wiring are good, check the seat occupant classification module and SRS control module communications and connectors. Replace the faulty module only after confirming upstream wiring and connectors are serviceable.
After any repair, clear codes, perform calibration or occupant classification learning procedure if required by manufacturer, and verify repair by re-checking for codes and observing proper occupancy detection during tests and road test.

Likely causes

Corroded/loose connector under passenger seat
Damaged wiring from seat movement (seat rails) causing intermittent/continuous open or short
Failed sensor mat due to moisture or wear
Connector pinned incorrectly after a repair or seat removal