Is the car as delivered or have you added any electronics? Boom box, speakers, amp, etc? Your PCM is a computer with several high capacity transistors driving the coils. Sometimes adding electronics to a car can create a ground plane fault that will not allow the coil drivers to go to zero. There's a lot more to it but the bottom line is it can create a lot of heat in the coils/wiring. A fresh coil can tolerate this for a while but the heat will get it sooner or later. It's why there's a warning about adding stuff to the electrical system of new cars. Good luck.