Rear Wheel Sensor
This is a very easy job that you can do yourself. The part costs between $35. 00 to $40. 00 depending on you dealer.
It's located on top of your rear differential in the middle. It should be the only electrical connection.
Just disconnect the harness from the sensor, remove a reatining nut that holds a small metal shield which also holds the harness in place, and then remove the bolt which holds the sensor.
You'll have to twist it a bit and slowly pry it out. The entire process shouldn't take more than 15 minutes.