Service engine light is on most of the time. Tech finds nothing wrong. on 2002 GMC Sierra 1500

Service technicians have checked repeatedly and find nothing wrong.

Asked by for the 2002 GMC Sierra 1500
2 answers
if the light is on there has to be a code.poss need a better scanner.some of the smaller scanners can't read all data
My car was doing this--turned out, it was the gas cap not seating well--cap was not turned enough times to tighten. (You may have to turn off ignition/turn on/turn off a few times for the light to go off if the cap is the issue).