Some codes...GM has a proprietary list they won’t share. I don’t remember which one stung me recently, but my regular mechanic had to take my Trailblazer to the dealer to obtain the definition. It is only going to get worse.
Their are certain websites that have the codes of all the manufacturers............
http://www.obd-codes.com/trouble_codes/chevrolet/index.php
What year is your Trailblazer?