...page 1-3 of the Owners Manual describes it as:
L. Light Sensor. See Automatic Headlamp System on page 6-3.
...and page 6-3 says this:
• Automatic Headlamp System
When it is dark enough outside and and the exterior lamps control is in the automatic position, the headlamps come on automatically. See Exterior Lamp Controls on page 6-1.
The vehicle has a light sensor located on top of the instrument panel. Make sure it is not covered, or the headlamps will be on when they are not needed. The system may also turn on the headlamps when driving through a parking garage or tunnel.
...but, page 2-10 has the answer (ta-da)!
• Immobilizer Operation
This vehicle has a passive theft-deterrent system. The system does not have to be manually armed or disarmed. The vehicle is automatically immobilized when the key is removed from the ignition. The system is automatically disarmed when the vehicle is started with the correct key. The key uses a transponder that matches an immobilizer control unit in the vehicle and automatically disarms the system. Only an authorized key starts the vehicle. The vehicle may not start if the key is damaged.
The security light, located in the instrument panel cluster, comes on if there is a problem with arming or disarming the theft-deterrent system. When trying to start the vehicle, the security light comes on briefly when the ignition is turned on. If the engine does not start and the security light stays on, there is a problem with the system. Turn the ignition off and try again. If the engine still does not start, and the key appears to be undamaged or the light continues to stay on, try another ignition key. If the engine does not start with the other key, the vehicle needs service. If the vehicle does start, the first key may be damaged. See your dealer who can service the theft-deterrent system and have a new key made.
Do not leave the key or device that disarms or deactivates the theft-deterrent system in the vehicle.