B2100low severityBody
Automatic Headlight Sensor Circuit
on 2019 Mazda MX-5 Miata 2.0L I4 · RWD
What this code means
Malfunction in the automatic headlight ambient light sensor circuit.
Symptoms
- Auto headlights not turning on in tunnels/darkness
- Headlights on in bright daylight
- Auto headlight feature disabled
- Dash light sensor not adjusting brightness
Common causes
- Faulty ambient light sensor
- Sensor covered by dashboard object
- Wiring damage
- BCM auto-light module fault
- Sensor window dirty
Diagnostic steps
- Check light sensor reading with scan tool
- Clean sensor lens on dashboard
- Inspect sensor wiring
- Test BCM auto headlight output
- Verify feature is enabled in settings
Repair notes
Replace ambient light sensor or clean sensor window. Check that nothing is covering the sensor on the dash top.
Other Body codes on this vehicle
B0001
Driver Frontal Stage 1 Deployment Control
B0002
Driver Frontal Stage 2 Deployment Control
B0003
Passenger Frontal Stage 1 Deployment Control
B0004
Passenger Frontal Stage 2 Deployment Control
B0005
Driver Knee Airbag Deployment Circuit
B0006
Passenger Knee Airbag Deployment Circuit
B0007
Rear Left Side Airbag Deployment Circuit
B0008
Rear Right Side Airbag Deployment Circuit
B0009
Rear Center Airbag Deployment Circuit
B0010
Driver Side Airbag Deployment