Amongst the host of issues with my 2007 Entourage is the back-up sensor/alarm which doesn't work (again). Last time it went on the blink, I brought the car to the dealer only to be told that it does work (and when I picked up the car, it actually did). - Since then, it's on the blink again. Constant beeping as if something were behind the car. The beeps are the same whether or not anything is behind the car or not and/or how close. The car is now beyond the warranty, so how do you fix this yourself?