I've got a similiar problem with my 2000 Grand Prix
The heat in the car works very sporadically (almost as if it only comes on when it "feels like it") and the "low coolant" light stays on when there is coolant in the system (or I have a leak I cannot detect)..
If you have the Dual electric climate control the smallest bump or movement of the knobs till turn on the system, but if not im not positive of what may be the problem
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