Check engine soon light comes on and off at random

[xtra]

I have a 1990 GMc K2500 Sierra where the service engine soon light comes on and off at random. Sometimes while driving it would come on. Then I turn it off and next time I turn it back on the light is gone. Just now I was driving home and it came on again. It went back off after couple minutes of driving tho. Any idea what it could be?
I just cleared the computer to check if it come back on. I also read the codes but all I got was 12 which doesn't indicate a problem. I will check the codes again tho.

 

[Drunkcanuk]

Well....check the code BEFORE you clear it and we will go from there.
They do go on and off, mine will do it if I get on the gas hard then shuts off a few seconds later.

I have a 1990 GMc K2500 Sierra where the service engine soon light comes on and off at random. Sometimes while driving it would come on. Then I turn it off and next time I turn it back on the light is gone. Just now I was driving home and it came on again. It went back off after couple minutes of driving tho. Any idea what it could be?
I just cleared the computer to check if it come back on. I also read the codes but all I got was 12 which doesn't indicate a problem. I will check the codes again tho.