I have a 1991 K5 4x4..I can drive for about 20-30 minutes then the service engine soon light comes on and stays lit.. after I turn off truck for a while light will go off then same thing drive 25-30 minutes it comes back on again..i am taking it to auto zone tomorrow but any ideas before then?

 

went to auto zone they said truck had to be a 96 model or newer to get reading from it..?? anyways..I changed the temperature gauge (it was broke) and the light quit coming on..easy fix..for once

 

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