B0166
Speedometer Signal Circuit Malfunction
Moderatesensor
Overview
The B0166 diagnostic trouble code indicates that the body control module has identified a speedometer signal circuit malfunction issue. This code means a body sensor or its circuit is not providing expected readings. Accurate sensor data is important for proper operation of safety and convenience systems throughout the vehicle.
Symptoms
- Parking sensors not detecting obstacles
- Auto-dimming mirror not responding to light changes
- Seat occupancy sensor showing incorrect status
- Door ajar warning when doors are closed
Common Causes
- Failed rain or ambient light sensor
- Camera lens obstructed or damaged
- Physical obstruction blocking sensor
- Door ajar switch stuck or misaligned
Diagnosis Steps
- 1Connect an OBD-II scanner and read all stored body control module trouble codes
- 2Inspect the affected sensor and its wiring connector for damage or corrosion
- 3Test the sensor resistance or voltage output with a multimeter
- 4Check for physical obstructions, contamination, or misalignment of the sensor
- 5Verify sensor calibration using scan tool where applicable
Estimated Repair Cost
$50 — $400
Cost varies by vehicle, location, and repair shop. Includes parts and labor.
Commonly Affected Vehicles
Subaru ForesterNissan PathfinderChevrolet TraverseFord Explorer
Related Codes
More Sensor Codes
P0070Ambient Air Temperature Sensor Circuit
LowP0071Ambient Air Temperature Sensor Range/Performance
LowP0072Ambient Air Temperature Sensor Circuit Low
LowP0073Ambient Air Temperature Sensor Circuit High
LowP0074Ambient Air Temperature Sensor Circuit Intermittent
LowP0095Intake Air Temperature Sensor 2 Circuit
LowFrequently Asked Questions
A stuck or misaligned door ajar switch is the most common cause. The switch is located in the door latch mechanism and can be cleaned or replaced for $20-$100.