How do I perm turn off "service engine soon" light on a 2003 Chev Trailblazer?

Disconnecting the battery will not clear a code from an OBD II system. The light is on due to a detected fault in the monitored emission control systems. It could be something as simple as a bad/loose gas cap, or something as serious as an engine control sensor that if left unrepaired may cause serious engine damage. Autozone sometimes will do a code scan for free. I suggest you find out what the code stored is, so as to not possibly damage your vehicle.

Unless you are a certified GM Tech, you have no idea if the light is on for a major problem or not. Take it to autozone or another "shade tree" mechanic and they will most likely pull the code for free. The problem with this is that they may not be able to tell you all you need to know about the code in the computer. Left unattended this "annoyance" may cost you and engien or transmission. Get it checked out.

You cannot permanately turn off the light as it is used for so many sensors.

Unhook the battery for 5 mins or so.

...Unless there's something *wrong* causing it to come on... You can always have an auto parts store (autozone and advance auto both do it for free) pull the code it's throwing to make it come on.

A lot of times it turns out to be a loose gas cap :P

you can not permanetly make light go off,it only comes on when theres a problem minor or major one autozone will scan it for free to see what codes are stored

small pice of electrical tape placed over the light