The low coolant light keeps coming on but the reservoir is full, what is causing this to happen?

If your coolant reservoir is full and the low coolant light is on, it is probably your coolant level sensor. If your low coolant light is on, and your reservoir is low....your are loosing coolant somewhere.

Your overflow tank(aka coolant recovery reservoir) is low on coolant. The coolant expands when warm and raises the level in the tank, which turns off your light. Top off the reservoir (when cool) to the "Full Cold" line. If you have to keep adding on a regular basis, then you have a leak somewhere in your cooling system, could even be the reservoir itself.

The CHECK COOLANT indicator illuminates when the coolant level is low in the coolant recovery reservoir. The low coolant level switch is probably in or on the coolant reservoir !

In most newer chevys, the coolant reservoir is part of the pressurized system. Rather than just holding overflow coolant and relying on the radiator pressure cap to draw from and expel to the reservoir, it is an active part of the cooling system. On these systems, there is a coolant level switch in the reservoir. This will activate if the level in the reservoir gets below a certain point. So it is possible to have a full radiator and still get a low coolant light. Be advised that as the reservoir ages and get stained, it is not uncommon for the low coolant sensor to give false indications of low coolant.

the coolant light needs water to keep the light off. Check the coolant level in the radiator and not the reservoir. If the wire to the sender unit is broken or not making good contact then the low light will also come on.

check your temp sensor

Bad coolant level sensor on reservoir, stalling may be a torque converter lockup issue.

Hi:
That warning light comes on when the level of coolant in the plastic reservoir tank becomes low. It is possible that the tank just needs topped off after the work on your car was performed. Basically, check the coolant and fill as needed, then keep an eye on your level to make sure there are no leaks on your vehicle since it was worked on.

the sensor is stuck, it works like your home toilet

I had the same problem and they suggested that I add GM tabs to the collant system to keep it from and very slow and tiny leak. They added the tabs and the low coolant light stopped.