my friend was coming home from the mountains and he decided 2 let the car roll on neutral. Than he stopped by a gas station 2 fill up and he saw smoke coming off of his hood, and his check engine light came on. I think that his torque convertor might of overheated or sumting. O ya its a front wheel drive. What do you guys think it might be?

well what other symptoms did it have? was the smoke coming from his engine?

Can't help too much without knowing where the smoke was coming from, or what kind of car even.

Alot of FWD cars have pressure lubed final drive assemblys in the transmission. The car needs to be in gear when the front wheels are turning at high speed. Fuel economy will actually be better too if you can just ride the DFCO all the way down the hill.