99 Suburban - Whitsend!
 

My parent's have a '99 GMC Suburban that is driving them crazy. The passlock keeps shutting the vehicle down. It is a K1500 with the 6.5
Turbo Diesel engine. They bought it new in '98 and now has 225k miles on it. We have hooked it up to the Tech 2 twice and have put a new lock cylinder in it and the lock cylinder housing containing the Passlock sensor, to no avail. In addition we put one of the DEI 555L Bypass Modules, still the security light will not go off. Where do we go from here? Please help. Thank you.

By the way, the truck still runs with the security light illuminated.

Welcome to the forum.:) By "passlock keeps shutting the vehicle down," I assume it cuts off shortly after starting. When the Security light is on steadily, there's a fault in the Passlock system and thus it goes into the fail enable mode which allows the vehicle to be started and driven. Maybe there's an intermittent or marginal electrical connection. Try simplifying the wiring to the DEI module. The DEI module should get the battery voltage over the RED/WHT wire and return the Passlock signal voltage over the YEL wire. Then, try grounding its ground wire to the good chassis ground instead of (or in addition to, if easier) splicing it to the ORG/BLK wire.