It was just a matter of time. All right, the check engine light'* on in my car, and it won't go away; when I turn on my car, there it is, lit up yellow. Now, while I'm waiting for my order from ScanTool.net to arrive, I'd just like to know how my MIL works.

Does it turn red or blink for severe problems?
Does it just turn on and stay on for moderately important stuff?
Does it turn on but then turn off when the car is shut off for the little things?
Can it turn off and clear the fault condition if the problem is corrected or no longer detected?

I'd just like to know how severe the problem is, so I can drive accordingly. (Like not yellow-lining the tach, for instance.)

First of all, the owners manual has all that good info.

But, if the light is just on, then the car is in no iminent danger. If it starts flashing then you got a little problem sometimes. When I first got my reconfigured PCM, I had it floored in triple digits and the light came on and started flashing, but it quickly went away when I left off the gas. Never did it again, so this could be just something idiotic that came on in your car. Like the gay light I got on now about Exhaust Gas Recirculation. I think if you disconect the battery for a little while then it resets settings in your car, maybe it can shut off the SES light.

I'm pretty sure with the roll out of OBD II the code sets itself and will not go away until corrected (some codes) or until scanned and cleared (more important codes).

Seems like you are stuck with the light until your tool comes in. While your car seems to run right you might be doing damage. If the O2 sensor puked and now you seem to be using a lot of gas, you could be murdering your catalytic w/o knowing it. Or is could be a stupid thing that won't hurt your car.