Possible causes: PATS module/key, transmission range sensor, ignition switch, starter relay diode, starter relay, any wiring associated with any of these.
Another possibility: If you have a remote starter installed with its own PATS key and inductive pickup loop, there might be a fault in that system that is interfering with the PATS function of your starting system.
You will really need the EVTM and a voltmeter to effectively troubleshoot this.
Steve
