2011 Toyota Sienna Owners Manual - Page 401

2-4. Using other driving systems Disabling pre-collision braking Pre-collision braking disabled Pre-collision braking enabled The "PCS" warning light flashes when pre-collision braking is disabled. Radar sensor The radar sensor detects vehicles or other obstacles on or near the road ahead and determines whether a collision is imminent based on the position, speed, and heading of the obstacles. 308