My son's 2001 GMC Sierra p/u is being a stinker! From time to time the truck refuses to start. I noticed that the security light comes on along with powering up the rest of the vehicle, but the engine will not turn over. My son who lacks any patience has been taken to the cleaners having the electrical system to the alternator replaced. Still the problem exists. Old mom here believes that it is the security system that for whatever reason is kicking in and being fussy. Last time he was home on leave, this event occurred. I was able to get the keys away from him and go out and fiddle with the truck. After trying to start it in park, in neutral, brake on brake off, I tried then by shifting the position of the steering wheel. It started then but still not sure that this was the catalyst. So what do you think? BTW... the ignition key is standard issue... no chip. So what do you think? If it is a systemic problem with the security system? Can we disable it? Thanks! Hugs & Kisses!