throwing codes?
 

I was curious how I can check to see if my 6.5 tb tahoe is throwing any codes at all. The check engine isn't on but i'm not too experienced in code reading. Does the vehicle only throw codes if the check engine light is on? Or can it still be throwing codes if the light isn't on?

step 1: year of truck?

OBDI can be read with a paper clip, OBDII needs a scanner of some sort.

You can have stored trouble codes in history that are not active faults....