when i hook a scanner to my buick rendezvous it say security error. what is this

Alright, You'll need to find out why the security error is happening. Have you already tried another key? Does your scanner display anything besides security error? If you lock the car with the key fob, and unlock it with the key, does it trigger the alarm?

I have an 03 rendezvous and I bought it with a problem in the electrical, which is so hard to pin point because these days modern vehicles have so many wires and there is no way to find out where to even begin looking and most computers only tell you so much, usually never anything you need to know electrically. Then mine all of a sudden just stopped going down the road. Instantly I figured the fuel pump because I couldn't hear it turn on without turning over the engine like you should be able to. So I knew it was either the electrical to my pump harness or my pump. So I follow my wires from the pump to a harness connector that connects through the floor of the car right behind the driver seat on the floor underneath the carpet, you can unplug it from outside the car. And that exactly what I did to check the plug out, and as soon as I pulled on it, it popped off and it was like someone sprayed me with a hose, all the water from inside the car, anything from kids shoes, snow, rain and anything spilled would find its way right to that harness plug in like it was the drain to a damn sink. And every single pin and wire was corroded and rusted off to the point it messed all my electrical up in front and made my fuel pump go bad. I replaced the pump, and the wires and harnesses for about $100 on my own, and now it runs like it's new, but this time I could the plug in metal plate that clips (horrible design flaw) the plug down for the harnesses and caulked everything around it and actually ended up having to replace my whole up front interior because it was soaked with water. But anyway I'm willing to bet it's a problem on 100% of these Buick rendezvous. Check that, and also clean you mass air flow and air intake and everything that has to do with your throttle body and any fuel sensor while your at it.