My "95 Pontiac Grand Prix has had the coolant level sensor, located on the side of the radiator, replaced twice now by my mechanic. The “LOW COOLANT” light still comes on, sometimes dimly or flickering, frequently. The radiator is always full and the coolant recovery bottle is at the proper level. The engine temperature stays in the normal range once it warms up. What else could it be??
The only thing left is the wiring for the sensor. Loose connection, chafed insulation, etc.
Although, when you say the sensor was replaced twice - in how much time?
See post #19 at the bottom of this link:
The problem showed up again within a week (wife’s car, doesn’t drive much). I had it replaced again within 30 days.
You probably need a coolant flush. These low coolant sensors that are mounted in the rad get contaminated pretty easily.
See pete p’s comment below which is what I was thinking. I don’t know this sensor’s design but they are often just electrodes where the coolant completes contact. The electrodes can easily pick up certain kinds of contaminants out of the coolant. Then they can’t pass the signal.