1995 Monte Carlo Low Coolant Light

My low coolant light has been blinking on my '95 Monte Carlo, but the coolant level is full and no overheating problems. I've heard there is a sensor that occasionally gets gunked up - does anyone know where this sensor is so I can troubleshoot? Anyone else seen this problem and have ideas what could be causing the low coolant light?

the sensor is located in the passenger side radiator tank about 1/3 the way down. Instaled, it looks like a little box about an inch square with a wiring harness attached. There is a retainer clip that holds it in.