Theft light flashes

[drrigg]

I've got a '98 GT that had some "check engine" issues which I have fixed and I disconnected the battery to clear the codes. But now the theft light flashes while driving and, if I lock the doors, the alarm goes off a few minutes later. This is annoying. Any ideas what I need to do?

 

[Jrgunn5150]

Try resetting the ECU again?