Quote Originally Posted by BigNick73 View Post
On the newer ones you need to turn the lights on and try to start it with the battery disconnected or wait a really long time to fully drain the system. Otherwise it'll hold the information. Also car may run rough for a minute or gas mileage drop for a short time when it restarts after this as the computer needs to relearn what setting it had before.

OBD scanners are so cheap now that it's almost pointless to not have one though, and then you can reset it yourself w/o all the hassle.
I have had cars come in with codes, disconnected the battery started taking stuff apart, waited on parts and days later got the vehicle back together and the codes were still in the system.

If you turn off your PC computer do you lose all the information stored on it?