Hello guys, I'm new to this sight although I have utilized similar forums in the past for other vehicles that I had (Fords). I have come full circle and returned to a GM product after having driven Ford products for the past ten years. The problem I am having is that I recently purchased a 1993 GMC Sierra 5.0L 4x4 after selling a 2001 Ford Mustang GT. The Sierra has been smoking slightly when first cranked as if valve ring seals need replacing which I intend to fix as soon as the hunting season here in Georgia is finished at the end of December. The other day while driving the vehicle a "Service Engine Soon" light came on and stayed on. The truck was due an oil change so I changed the oil, unplugged the battery for about fifteen minutes to reset the ECU, and then plugged the battery back up and cranked the truck back up. The truck ran for about five minutes without the light on and the light then came on again. I have noticed no differences in the way the vehicle drives or any other performance issue that would relate what this light is about. I have not yet tried to pull a code on the truck and wasn't really sure if that could be done on this vehicle as the only Chevy's I have ever had were older (70's and 80's) models and I have been working on the Modular Ford motors that I have owned for the past ten years. I am not completely sure what the issue could be, other then possibly an o2 sensor, however, less simply throwing money at the problem and hoping it fixes my problem I have no idea where to begin. I also thought that maybe the issue was a fouled plug(s) from the smoking but as I said before I really am not sure. Any help or advice would be greatly appreciated.