[misslindseysue]

Um... yeah. A Tech II (not sure about a generic scan tool - I should try mine) will tell you which one it is. And the hub can go on either side, so you could buy one first, then try plugging it in and seeing if the light went away. But... best to scan and find out for sure. I was convinced that it was the right, bought the part, brought it to the shop, and they called... "code says left, you still want to replace the right?"
A dealer might scan it for you for free if they're feeling nice and aren't busy some day. Just roll in like "these lights came on, can you quick scan and tell me if it's anything I have to do something about right now?" I've had some dealers scan it for me no problem, and some will try to make you make an appointment or pay for it. In that case I just took it to autozone and used a gst (generic scan tool).