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Ill ask my question as simple as possible....
On my Pontiac Grand Prix, my Low Coolant light is on and doesnt seem to go off.

What i have Checked:
Coolant(radiator) Level - topped off
Coolant(resivour) Level - correct level.
Check all hoses and connections for leaks - Found none
Used a Presure device to manually add presure to search for leaks - found none
The heat works in the car
everything else seems to be working
Car does NOT overheat, the light just doesnt go off.


What i have replaced:
Replaced the Coolant Level Sensor that is located on the Radiator (little square device $60 bucks)
And topped off all fluids.

What are some other things i could check?

Thanks in Advance.  

Just a bad sensor in the plastic coolant reservoir.  

DO you know if i have to get a whole new container or just the sensor for the container?  

Thanks, I didnt know Grand Prix's had sensors in the plastic tank as well.  I will take it out this weekend and see if i can clean it up before trying to buy a whole new one.  Maybe the sensor is clogged with gunk!  Most likely it is. Thanks.  

After thinking about this post I come to realize that the sensor is mounted on the rad.  sorry I didn't  get back to you sooner.  

Disconnect the battery ground (negative) cable.
Partially drain the radiator.
Disconnect the electrical connector from the coolant level module.
In order to unlock the coolant level module, lift one leg of the snap clip from its locked position and pull outward with a slight twisting motion. Remove the coolant level module.
Lubricate the O-ring seal with coolant.
Place the snap clip leg in place.
Install the coolant level module.
Connect the electrical connector to the coolant level module.

Important
To properly fill the system requires the use of the air bleed vents. Refer to Draining and Filling Cooling System .


Fill the radiator. Refer to Draining and Filling Cooling System .
Connect the battery ground (negative) cable. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical.
Inspect for leaks.  

I have a 2002 Grand Prix GTP that has the low coolant light come on for a period of time and then goes out.  I was reading your response along with the others but couldn't tell if you were talking about the coolant level module being in the radiator or the plastic fill jug as indicated in an earlier comment.  I assume you meant the radiator since you instruct to drain it.  Also, are you saying to replace the coolant level module or just clean and lubricate the O-ring?  

that's probably not your problem. the intake manifold on the pontiac grand prix and grand am are notorious for going bad and the average cost to have it fixed is about 1000.00 or higher. and to make things worse, the problem keeps happening!! my mom had hers replaced then later had to replace the motor because of it, and now it's doing it again! so you might as well tell GM "thanks for telling me to bend over."  

LOL.... i recently went to do an oil change on my 2000 pontiac grand prix at mercury blvd in hampton VA at a GM chevy dealer shop. the only light that was on was the "change oil soon". but the next day the "low collant" light would stay on for a while. i went back the next day. they said the was collant coz the collant reseroir was empty. it looked like it was refilled at all from the oil change. quoted $900.00 to fix leak. i advice to check if leaking and to put coolant in the reserior. came back the next day and showed them it wasen't leaking (the coolant level didn't move from where they filled it) and that they forgot to refill coolant.excuses. excuses. and more excuses. quoted for the coolant sencor $80.00.then i noticed one of the other fuild wasen't refilled and i pointed it out. more excuses. then they filled it. all in all. bad expirience. seems like they are trying to get away if they can to save money. in return we, the consumer suffers. (car breaking down, etc...) if coolant sensor didn't come on i would have gladly filled the coolant fuild my self and whatever fuild my car needed. $30.00 oil change. they would not do something about the "low coolant" light. My first oil change at a GM dealer. will not go again.  

First,the 3100,3400 or 3800?The 3100s and 3400s have problems with intake gaskets,factory ones are plastic and Dorman fixed that with a kit.The Dorman intake gaskets are made out of metal instead of plastic.If the 3800,the upper intake is a huge problem and does not cost a grand to fix.I have done a lot using the upgraded dorman upper intake.Cracks at the EGR port and fills the intake full of antifreeze,will cause the vehicle not to start.It fills the cylinders up with antifreeze too if not caught in time requiring removing the spark plugs and turning the engine over to get the anti freeze out.Pitch and replace the spark plugs at the same time when not caught in time.