[GWAGON_99]

I know that Hummer offers a backup sensor that goes in the reciever hitch. I'm not sure if it hooks to the radio or what but I think it is around $400 and since Hummer is a GM it might be compatible with your Sub.

 

[GWAGON_99]

So here is the scoop on the Hummer (possibly GM???) Backup sensor. It plugs into the Rec. Hitch and plugs into the trailor light adaptor(power). It then has a little reciever module that plugs into a cigaret lighter and beeps as you approach an object. The one I know of says Hummer on it but I'm sure that they make them for other vehicles or just plain. We put ours on with a locking pin of course so they can't just be taken out. (common sense I know but it never hurts to say)