2000 Cavalier service light on

Hi my sons service engine light is on in his 2000 cavalier 2.2L, auto. I tried reading the code but nothing, my code reader would light up as soon as you plug it in but on this car it dosn't till I press the read button no code there. Could the computer be no good if so how can I test it?

You may need a bi-directional scanner capable of reading SIR, transmission, and body codes. The lamp may be on due to something other than the powertrain.

Thanks for the info, I'll see if I can find one or take it to a shop.