On the 300M,Grand Cherokee and minivans we use a magnet that fits around the valve stem to reset sensors.This reset also tells the computer where the tire is located...front , rear,spare..The crossfire doesnt have this set up or overhead display so when the light comes on you have to check all tires.When you set tire psi's you must drive car to reset.The tire sensor is part of the valve stem and is held on by a nut it will reset itself on the crossfire or should!The goverment wants these sensors on all cars and chrysler will soon use the ABS wheel speed sensor as a trigger to save money.A tire with less air will turn slower and the ABS sensor will pick it up and turn on light.