service engine soon light

1990 k1500 350 4x4
Just for the heck of it I replaced the mass air sensor. Since then the service engine soon light comes on after about 15 min. of driving?
Why?

I didnt think a 90 truck had a mas? I think they have a map. It reads vaccuum. You could have left a hose loose, or maybe you just need to reset the computer. Unhook the battery for a few minutes, that will reset the codes.

Thanks, it just happens that I bought a code reader and it suggested to do the same and so far its O.k.