Why does my truck show blinking security light and wont start

There are a couple of reasons this can happen. Basically something is tripping your security system to prevent the truck from starting, the security system is thinking the truck is being stolen. When it happens, use your remote lock/unlock key fob. Exit the truck and use the fob to lock the door. Hit the lock button 2x so the horn will chirp, then unlock it with the fob and try starting the engine. Also, some models may have a security chip in the key itself. The chip may be going bad. Check with your local GM dealer to see if yours has a chip. A new chipped key may be needed. Good luck.

Sounds like the "chip" in the key or the ignition sensor may be bad or going out. You should be able to take it to a dealer and have it checked for little cost. If you have a spare key, try it. It may work fine. Hope this helps, Mike

I've had one do this before after an accident and I changed the steering column. I had to trailer it to a GM dealer and have them link it up with the factory to rewrite the data on the pcm. It only took about 10 minutes to do it. It's a safety feature and part of the security-anti-theft system. If you talk to the service dept. at GM, sometimes they can tell you to do certain things to reset it if something happened to cause it like a dead battery.