My right rear sensor has been acting up for a few months now. I've tried everything from disconnecting the batteries, reseting the sensors and switching tires around. I still get that damn error on the first 20 miles on the highway and it comes and goes from there. I'm not worried because I've ordered new wheels and tires and will be getting that gadget from H&S that allows you to shut the system off. Hope you have better luck than I.
Also look in the manual to see how you reset the sensors with that little button in the owners book. You have to press brake, cycle ignition a few times, press and hold brake and then cycle keys again. Then you come around with that tool and reset every sensor at the tire.