B3066

Code

Generic B — Body

Occupant Classification Sensor Circuit Low Voltage

Brand: Generic

Type: B — Body

Views: UK: 21 EN: 37 RU: 27

AI status

Completed

ready

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Page language: EN

Causes

Short to ground in sensor signal or reference circuit
Open or high-resistance connection in wiring or connector
Failed occupant classification sensor (pressure/weight mat or strain sensor)
Low or missing reference supply (5 V) from control module
Corroded or contaminated connector, water intrusion
Faulty occupant classification control module or related ECU

Symptoms

Airbag warning light illuminated
Passenger airbag enable/disable status may be incorrect or disabled
DTC B3066 stored in SRS / occupant classification module
Possible intermittent fault when seating position or weight changes
No obvious mechanical symptom other than warning lamp

What to check

Read stored codes and freeze frame data with a capable scan tool; record related SRS/occupant-classification codes
Perform visual inspection of seat bottom and underside wiring, connectors, and sensor mat for damage, corrosion or contamination
Check for aftermarket seat covers or loose seat components that could affect the sensor
Backprobe and measure reference voltage (typically 5 V) at the seat sensor connector with ignition ON
Measure sensor signal voltage with seat empty and with a known load (sit or place weight) to confirm response
Check connector pin continuity and resistance to module ground; perform wiggle test while monitoring signal

Signal parameters

Reference supply: typically +5 V (check vehicle-specific spec) present at sensor connector with ignition ON
Sensor output: normally varies with occupant weight (commonly in the 0.5–4.5 V range depending on design)
Low-voltage fault: signal below expected threshold (often
Ground continuity: good chassis/ECU ground at connector (near 0 Ω to low ohms)
Sensor output should change measurably when weight is applied/removed

Diagnostic algorithm

Use a scan tool to confirm B3066 and note any related SRS/occupant codes. Clear codes and reproduce if needed.
Visually inspect the passenger seat, underside cover, and wiring harness for damage, loose connectors, or water intrusion.
With ignition ON (and SRS power enabled as required by vehicle procedures), backprobe the sensor connector and verify the reference voltage (typically 5 V) and ground presence.
Measure the sensor signal voltage at the connector with the seat empty and while applying a known load (sit or place a test weight). Confirm the signal changes and is within expected range.
If signal is low or stuck, perform continuity/resistance checks between the sensor connector and the occupant classification module to find opens or shorts. Wiggle the harness and connectors while monitoring for intermittent changes.
Inspect connector pins for corrosion, bent pins, or poor mating; clean or repair as needed. Repair any damaged wiring with proper splices or harness replacement.
If wiring and connectors are good but signal remains low, replace the occupant classification sensor mat per manufacturer procedure and retest.
If new sensor does not restore normal operation, suspect the occupant classification control module (or airbag module) and follow manufacturer procedures for module testing and replacement. Check for Technical Service Bulletins (TSBs) before module replacement.
After repairs, clear codes and verify proper system operation and that the passenger airbag enable status is correct.

Likely causes

Damaged wiring harness under the seat (pinched, chafed, or severed)
Corroded connector at the seat sensor or module
Failed occupant classification sensor mat
Blown or poor internal reference supply from the airbag/occupant classification module

Fault status

⚠️ Status

Occupant Classification Sensor Circuit - Low Voltage detected. Passenger classification signal is below expected threshold; may disable passenger airbag and illuminate the airbag warning lamp.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours