01 Chev Silverado Passlock

I was wondering if anyone would have info on how the GM Passlock system works, spec, etc. The truck I am working on is a 2001 Chev Silverado 1500, 4.3L with automatic. I doesn't have power locks, windows or keyless entry. The truck also has 147K on the odometer. I work in a general auto repair facility. I generally don't install alarms or stereo systems. The customer complaint is that the truck has a variable start. Sometimes the truck will crank but will not fire in the morning. He said if he lets it sit, most of the time it will start then. The truck is used for tire delivery. He has been on a delivery where it has started all morning and then wont after making a stop. I have checked out the obvious checks. I hooked up the scanner and had code P1631 for Theft system password incorrect. I have talked to the dealer about what is going on and they told me that the ignition switch and/or the housing can be worn enough to cause the no start. It seems like getting any info on this system is impossible. I would appreciate any info and  I don't mean to venture off into territory that this site doesn't deal with. Please email me at super64belair@yahoo.com if you have any info. Thanks.

has this vehicle had a remote starter installed?Kevin Gerry

Certified Electronics Technician

MECP First Class Installer

Owner/Installer

Classic Car Audio

since 1979