I was doing some research last night I'm finding it is really easy to find the ABS front wheel speed sensors but the rears are extremely hard to find. I found a couple sets for sale on ebay but you can't find them new. I read at a few places that they've been discontinued. I know these things go bad over time just not sure how long the wheel sensors last. I might have to buy one of the sets off ebay to have shelf spares.