Ford Repair: Help diagnosing a transmission (i think) problem., trouble code, auto 4x4

Question
I have a 2002 Ford Escape V6 auto with auto 4x4. I am selling it and a guy came to look at and took it for a test drive. When he came back there was a light on, on the dash. The truck now will not rev past 2500-3000 RPM There is no reverse and will barely go forward. It seems as though it is stuck in O/D and don't know where to start. Any Help would be muchly appreciated.

Answer
We need to know what the light says.You can go to you're nearest parts store to have it checked for free,providing the vehicle will drive safely.If not,then you can buy the same scan tool they use for around a hundred bucks.Take it back after you're done.My guess is that there is a sensor down for the transmission,but I can only guess without the trouble code.Get all the information you can and let me know.