“What’s the difference between Pre-Collision and Advanced Pre-Collision? Are they the same system?”

Lexus customer assistance has noticed that many owners ask this question right around the time they’re looking for a new vehicle. So here’s a quick primer to take on your next model search.

Basically, the optional Pre-Collision System (PCS)[1]—available for most models (not the LFA or SC)—is Lexus’ collision-detection and collision-preparation system.

As you drive around, PCS sends out radar signals in front of the vehicle, which detect other cars, like, say, the driver ahead of you tapping the brakes too hard. PCS uses those signals like a physics professor on a caffeine high: it constantly, and quickly, calculates the distance and speed of vehicles in your path, and determines whether or not you stand a chance of bumping into any of them.

Lexus Pre-Collision System (PCS)

If, say, the time comes when PCS determines that a frontal collision is unavoidable, the system then braces you for impact: it automatically tightens the front seatbelts and preps the Brake Assist[2] system so you’ve got extra braking power the second you respond the way most of us do when ours cars are about to hit something—slam the brake pedal.

“The whole idea is to get the vehicle and driver ready for the accident if it’s going to happen,” says Charles Hubbard, senior dealer education administrator at Lexus College.

Okay, so that’s PCS. Where does the Advanced Pre-Collision System (APCS)[3] fit in?

Driver Attention Monitor

APCS, right now an option for the LS and LS hybrid, gives you everything PCS does, but has a couple of big extras. Numero uno is the Driver Attention Monitor, which employs an infrared camera behind the steering wheel (see left) that literally knows where your head is at. In other words, while the PCS radar sensors and computer are watching the world ahead, this little extra is helpfully watching you.

If your face is turned away from the road when the system detects a potential collision, the Driver Attention Monitor warns you and, if necessary, gently applies the brakes. And, of course, if a collision is deemed unavoidable, the same PCS measures go into action: Brake Assist gets prepped and the seatbelts get tightened.

Finally, APCS also comes with an Active Pedestrian Detection System[4], which allows the vehicle to “see” people, thanks to four stereo cameras, as well as extra infrared technology that enhances nighttime object detection.
source: http://drivers.lexus.com/lexusdrivers/magazine/articles/Vehicle-Insider/Ask-Lexus-Collision