DTC 21: Solar Sensor Circuit (Passenger Side): Notes
WARNING: This page is about a different car, the 2004 Toyota Camry. However, it is still accessible from the selected car via links, so may be relevant.
A photo diode in the solar sensor detects solar radiation and sends signals to the A/C amplifier.
Fig 1: Identifying Photo Diode In Solar Sensor Detects Solar Radiation & Sends Signals To A/C Amplifier