Two problems related to anti-theft controller have been reported for the 1999 GMC Yukon. The most recently reported issues are listed below.
My vehicle will not start periodically while it is raining or the humidity is very high. During this time, the security light will blink and you must wait a minimum of 10 minutes before it will start again. There has been one case when the car completely stopped during driving and lost all power (steering, brakes, etc). The dealer could not find out why this was occurring. The key cylinder was replaced based on a "passlock" error code in the ecu. This has not resolved the problem. I have visited many websites and found this to be a pretty common problem with Chevrolet and GMC suvs and across many years of production.
Gm has an anti-theft device called a passlock. The systems seems to be faulty on a very large number of their vehicles. It makes the auto not start and maybe even sometimes die while running. I'm quite concerned of the possibility of the engine failing while driving down the road. They told me it would cost $400 - $500 to fix it.