Automatic Headlight Sensor Circuit
2003-2009 Toyota 4Runner 4.7L V8
Description
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.
Related Codes
Other Body Codes
- B0001Driver Frontal Stage 1 Deployment Control
- B0001Driver Frontal Stage 1 Deployment Control
- B0002Driver Frontal Stage 2 Deployment Control
- B0002Driver Frontal Stage 2 Deployment Control
- B0003Passenger Frontal Stage 1 Deployment Control
- B0003Passenger Frontal Stage 1 Deployment Control
- B0004Passenger Frontal Stage 2 Deployment Control
- B0004Passenger Frontal Stage 2 Deployment Control
- B0005Driver Knee Airbag Deployment Circuit
- B0005Driver Knee Airbag Deployment Circuit
B2100 on Other Vehicles
Toyota 4Runner
2003-2009 4.0L V6
Toyota 4Runner
2010-2024 4.0L V6
Toyota 86
2017-2020 2.0L H4
Toyota Alphard
2023-2025 2.4L I4 Turbo T24A-FTS
Toyota Alphard
2023-2025 2.5L I4 Hybrid A25A-FXS
Toyota Altezza
1998-2005 2.0L I4 3S-GE BEAMS
Toyota Altezza
1998-2005 2.0L I6 1G-FE
Toyota Aqua
2011-2021 1.5L I4 Hybrid 1NZ-FXE
Common Questions
What does code B2100 mean on a 2003-2009 Toyota 4Runner?
B2100 stands for "Automatic Headlight Sensor Circuit". Malfunction in the automatic headlight ambient light sensor circuit.
What are the symptoms of B2100 on a Toyota 4Runner?
Common symptoms of B2100 include: Auto headlights not turning on in tunnels/darkness, Headlights on in bright daylight, Auto headlight feature disabled, Dash light sensor not adjusting brightness.
What causes B2100 on a 2003-2009 Toyota 4Runner?
Common causes of B2100 include: Faulty ambient light sensor, Sensor covered by dashboard object, Wiring damage, BCM auto-light module fault, Sensor window dirty.