What is wrong, no start, no key fobs working, light on?
the components of the Passlock(TM) system are :
the key has a value the sensor in the ignition cylinder sends to the bcm, once verified the bcm sends a signal to the pcm to enable to fuel.
you might try a new key but if any other parts are needed they will need to be programmed in. Complicated system, I would take it to a GM dealer so you don't have to guess. With out the Tech2 or GM mdi system almost impossible to diagnose.
No way to bypassthat I know of.