You can try this factory relearn procedure. If that fails to cure the problem, the system will have to be checked with a class 2 scanner that is capable of performing function tests. The system works through the body control module and a bunch of other electronic sensors. The system is pretty complex and there is not really much you can do at home in the way of testing or repairs. Give this a try, I hope it helps, but follow it word for word, no short cuts.
30 Minute Re-Learn Procedure
The vehicle learns the PasslockTM Sensor Data Code and/or password XXXXX the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.