Check engine light on

I have a 89 s10 pickup with a 4.3L and four wheel drive.The other night it died on me on my way home because the battery was just about dead.Before it died on me the check engine light wasn't on.But right after I started it up it was on.I don't know where to start with problems.Does anyone have any idea where I can start or what the problem could be?

Its letting you know your aternator is going bad.

I'll put it on the alternator tester to find out for sure.Thing is I just got this truck.The alternator looks about brand new.Could it be because it was low on oil?I think I gotta replace the oil pan gasket.

Its possible that it detected a drop in oil pressure and tripped the Check Engine light.

That's exactly what I was thinking.

I would also still check the alternator. Even tho it may look like it's new it could still be charging the battery 100%. That happened to me

No expert here but I had similar problems with my s10 blazer. New o2 sensor and EGR valve fixed that problem. Test the alternator for sure.