A faulty PCM will do all kinds of random crazy stuff, just about any problem a car could have would happen because of this, but very randomly. Expect random multiple CEL's for no reason, poor fuel mileage/misfire/knock (if the car runs at all). You could also have a fire in there. But most of today's PCM's have no reason to fail, that was a long time ago and electronics are much better. When you mess with them is when you risk trouble.
If you burned up some transistors in there it would smell aweful, like burned electronics do.