security issues 99s10

i have a 99 s-10 2.2 manual that has issues with the security light. About once a month the security light will start flashing when I turn the key on and will not let the truck start. If I wait a while and try again the truck starts. I have tried a new key but that does not seem to work. Does anyone have suggestions on what to check, or what to try? Thanks

Welcome to AF.
Do you have the standard anti theft pass key 111
or the horn and light flashing CTD system RPO code UA6?
Has any work or repair or body or pcm or anti theft key stuff been replaced or repaired on it?
I would suggest next time when it does get it in as soon as you can and get it checked for body codes past /history or present and post back code.
On the knew key you tried was it a original key or a new key you had made for it?
Also try the relearn procedure.
Key from off to on for 10 minutes.
Filp key off and repeat procedure 2 more times and see if it will start.

thanks for the reply, i am not positive about the key but I assume it is a standard key. Several people told me they have some kind of chip inside the plastic molding or something that relates to the security. Also as for horn and light flashing CTD system RPO code UA6, I am not sure what you are talking about but if it is on the dash i did not see any of this. If it isnt can you be more specific by what this means, thanks.
None of the the listed items have been repaired, also can you read body codes with the hook ups for the check engine codes or does that require a different system?
Both keys are originals. Thanks for your help, i will try the relearn procedure, does this process reset a computer? Just curious to how it works and what exactly it does. Thanks,

Dan

The relearn resets the anti-theft /body computer not the engine pcm to learn your key. The key has a coded chip inside.
To check or test or get codes you need a scanner that will read and check the body and anti theft systems.
A regular OBD11 scanner or codes reader like AZ uses will not do it.
The CTD anti theft system blows the horn and flashes the head lights system when set off.
Pass key 111 just shuts down engine when triggered.

thanks for the clarifications
the security system in my truck is the pass key 111 system. I will give the relearn trick a try, hopefully that will work, if not ill get it scanned thanks