2004 Rendevous ABS/Trac/Tire Pressure

Within a period of about two weeks, my fiance's Rendevous has started having "problems". First, we received notice that Trac was off. After driving the car for a while, shutting it off, and restarting, the indicator went away. Then, more recently, the ABS light has joined in the fun, and often decide to display their messages together. This week, we received notice about a tire pressure problem, of which there was none.

As these are all related to the tires, should I assume I've got some sensor module blown, and get ready to spend $500 on some replacement?

Thanks!