low coolant light on?

1996 gtp with the 3.4 dohc. low coolant light came on. coolant level in radiator is ok and level is up in the overflow tank. engine isn't running hot. does this light mean anything else? and where is the sensor?

The sensor is in the passenger side radiator tank, about 1/3 the way down. It's about 1-1/4" square. It's pretty common that they get gunked up with Dex-Cool sludge. GM part number is 10096163.