I've got a warning light problem

One of the lights switched on, it looks roughly like like a little rectangle with a line going through the top, located in the top left of the dashboard with the rest of the warning lights, to the left of the RPM and speed meter.

I don't have the manual, and I can't find it online either, so I'm in a bit of a situation. I thought it might be the coolant, but I just put some in and it's still on.

Can anybody help me?

Ok seems to be you're a victim of coolant consumption because an UIM failure, what model do you own?

'98.

I solved it by adding EVEN more coolant, and then taking it to a parking lot and revving the engine until it was force to use coolant. Guess simply turning the car on and checking the warning lights isn't enough.

For everybody else, what's a UIM?

Upper Intake Manifold, it'a a known problem for the 3.8 intrigues, if your car is "drinking" coolant at least once a week you might want to change it as well as the lower intake gaskets, with simple tools and a bit of patience, you can DIY, even if there's no consumption as a preventive maintenace so you are no left on the road (personal experience) you migh want to check this link:http://www.automotiveforums.com/vbulletin/showthread.php?t=701325