I am fairly sure the PATS key memory is programmed into the car's EEC computer, which is the one the mechanic probably changed. That would explain the key code. If that's true, the car won't even crank, just light up the red LED on the dash, if you try to start it. I got a key cut, no start until I programmed it. The original working key was needed, I am unsure what you do if the EEC is changed. Hopefully, the mechanic knows.(Dealer?)
