I went over to jump-start my neighbors Cavalier when he couldn't get it to turn over.
Once we concluded it wasn't a dead battery, he called the dealer.
A tech came over, pulled a circuit board, then clipped and spliced a wire. ... Car started !
Tech sez; "the anti-theft board that checks the key often fails without warning." Unless the owner wants the feature, it's easier ( and cheaper ) to disable and remove.
First thought; If the tech could disable the circuit in a few minutes, does the "key chip" really have an anti-theft value ?
Second thought; At one time, you had the key switch, and the starter solenoid. Now, there's the keyswitch, the anti-theft circuit, the "car in Park" switch, and, God knows what else. It's not a fix-it-yourself" thing any more.