reverse parking sensors

Anybody have any problems with their back up sensors not working correctly? I just bought this vehicle and the system does not work. The "OFF" light stays illuminated on the control button which I read in the manual means there is a fault code stored for it. I cant afford the $75 checkout fee from the dealer. Any ideas what the cause could be, I thought maybe there might be some common problem with these systems.

Check the connections to the sensors first. They are hinda hard to get to, but we had one that the sensors were not properly connected after rear bumper repair.

First and foremost, clean the sensors. Sensors don't know if it's dirt or a shopping cart behind you, all they know is that it's REAL close.