This 2002 Pontiac Grand Prix came in with a faulty coolant level sensor. The radiator was full of coolant, the light was on and it would go off when the sensor is disconnected. The sensor is in a pretty difficult place to access for replacement but there is a trick. The sensor is the grey cube located behind the transmission cooler line in the picture below.
The trick is to remove the passenger side headlight assembly. There are a couple of 10 mm headed bolts that need to be removed. The grey bolt heads can be seen at either side of the headlight assembly as seen in the picture below. There is also a Phillips headed screw that has to be removed in order to take the park/turn signal light assembly out first.
With the bolts removed the headlight assembly can be removed. It takes just a little gentle rocking and twisting to get it pulled from the body.
Now the sensor can be easily accessed through the body opening.
There is a wire retaining clip that needs to be removed. Then the old sensor can be twisted and pulled from the radiator. The new sensor simply pushes in until the clip snaps into place. I used a mirror to see make sure the new sensor is fully seated in the radiator.
Installed the head light assembly and then the park/turn signal light assembly.
A good look at the new and old sensors along with the retaining clip.