Service engine soon light

I am having some problems with the way my truck is running, I have been through all the normal tune up stuff ( cap, rotor, plugs, etc). Nothing seems to be helping, so I went and bought a code scanner and a book of codes so that I could check them out to see if there was a problem in the computer system.
Now I get ready to do this and I find that the service engine light doesn't work. So I checked the bulb and it is fine.
I do not know where else to look so if anyone has any ideas at all please let me know.

If the light doesn't work at all, does it come on during the bulbcheck?, it's probably the ECM itself. Older S10's where famous for this, try pulling it out and wrapping it with you knuckles and see what happens.

The decoder is set for your vehicle ?

Fuse ok ? IGN/GAU 20A, CRANK 3A, ECM/IGN 10A, ECMB 10A

You'll have to trace back the continuity (Brown/White) from the bulb holder to ECM, cleaning the connections as you go.