If you can find the module, possibly under left back seat or drivers seat if 2-door, am an idiot, don't know what you drive. Anyway, there is a sticker with the original code on it. Its a 5 digit number.
I took mine to the dealer, they did a two minute scan of the truck and told me the number. No charge.
2006 F150 XLT 4X4 SuperCrew, 5.4L 3V Triton V8
3.55LS,Trailer Tow Package, XLT Chrome Package
Power Pedals and Rear Window, 18" Stock Rims
Heated side view mirrors, Back up Sensors
My other vehicle is a John Deere