1990 Chevy Lumina Euro 3.1

Automatic, front wheel drive, v6, 66k miles

My question involves several symptions all at once. First this "service engine soon" light came on while I was on the road that caused no immediate problems. Second about an hour later the car decided it no longer need power steering fluid and dumped it all on the road. That was taken care of very quickly due to a convienent gas station and has not leaked since then although the location of the leak has yet to be found. It left a neat little 2 or 3 inch wide line from front to back on the inside of the hood of steering fluid. Lastly the car now has a noticeable off-line stumble that might have something to do with a miss at idle and when held steady at about 2000rpm. Now so far I have already checked the codes and only gotten a code "12" which as far as I can tell means nothing really. Also I hooked up a Snap-On scanner to the car which said it couldnt not find the computer at all. Please any information on any of these problems would be appreciated. Thanks, Greg