Light flashes security , wont start wait exactly

OK. you had the battery disconnected. Here is what you do. Turn on the key. The security light will begin to flash. Wait (about 10 minutes) with the key in the ON position. The security light will stop flashing. TURN OFF the key. Then, turn on the key and start the car. Security system is supposed to prevent theft for a 10 minute delay. This usually discourages any thief. This will work, You just need to be patient with the 10 minutes. It seems like an hour when you wait ten minutes for that security light to stop flashing.

When security light flash truck wont start, put ignition on and wait 10 minute security light will come on solid now it reprogram itseft truck will start, you will need a new key cylinder make it code to your key at the dealer

Is the security light flashing? If so, turn ignition on and wait for 10 minutes and light should stay on solid. Then try and start the car without turning the ignition back off. Then turn off ignition and wait 1 minute. Then turn ignition on and see if security light is flashing. If not try and start your car. If it is flashing, try waiting again with just the ignition on and see if it goes out.

I OWN a 2001 Olds Alero and the same thing happens to mine.. It's an easy fix..
1. Turn the Key to ACC (keep it in this mode for the entire 10 minutes).
2. The security light on the Dashboard will flash for exactly 10 minutes..
3. Once the 10 mins are over, the security light will stay solid..
Wait for the red light to disappear off the dashboard...
YOU ARE NOW READY TO TURN YOUR CAR OFF AND RESTART YOU CAR....

SIMPLE FIX..
I DO THIS ALL THE TIME TO MINE..

It's could be your PassLock security system that is failing. It started happening earlier this year on my 2002 Impala. If you wait about 20 minutes, it's starts right up after it resets. It started to happen every couple weeks and then every couple days, after a few months. I ended up bypassing the security by soldering in some resistors.

See the pictures at:
http://s2.photobucket.com/albums/y48/ZeeVert/2002%20Impala/PassLock%20Bypass%202011/
It took me about two hours to take apart the dash and carefuly double check everything I did, and take pictures. If I did it again... maybe 45-60 minutes (plus getting resistors).
I was lucky to have some resistors close to what I needed, so it cost me nothing but some time.

My ignition resistance checked at 1250 ohms. I used three resistors totaling about 1400 ohms. (At least according to my $10 meter).
Seems to work, even after I disconnected & reconnected the battery.

turn the key on and wait till the security light stops flashing ( this could take as long as 30 minuets ) then turn the key off then back on but do not try to start the engine and wait till the security light stops flashing ( again this could take as long as 30 minuets ) then turn key off then turn key on and start engine.

im just gonna take a stab in the dark here i understand that your security light is on try unlocking your door with your key sometimes you just need to reset the security. otherwise ive seen a security module go bad that may be preventing you from starting it.

it is a 2001 GMC truck a short bad

try disconnecting the battery should reset the system

Here is what you do, but only when the SECURITY light flashes - if it is always ON or OFF it's no use.
Turn the key in the ignition to ON.
Wait for exactly 10 minutes ( SECURITY light will flash for 10 minutes and then stay on SOLID)
Turn the key to OFF
Wait 5 seconds.
Turn the key in the ignition to ON.
Wait for exactly 10 minutes.
Turn the key to OFF
Wait 5 seconds.
Turn the key in the ignition to ON.
Wait for exactly 10 minutes.
Turn the ignition OFF.

Start the car normally.
It has relearnt the keycode and you're good to go.
NOTICE - it takes 30 minutes to relearn, that's THREE cycles of ON - 10 minutes - OFF.

Good luck.