I just bought a 2005 2500 duramax with 230k. Runs like a dream... until the low coolant warning came on. I have not noticed any coolant leaks under the vehicle. I think that the coolant is coming out of the overflow tube off of the expansion tank. It always is wet. I just took it on a 1200 kilometer trip pulling a 20 foot travel trailer before the warning came on. It does not overheat just warns that the coolant level is low.

 

My 2000 Impala is doing that, and there is no sensor in the overflow tank, so I don't know how it is sensing low coolant level. We went from Logan, Utah to Disneyland and back with that alarm coming and going, but the coolant level was never low. I only added water to make sure it wasn't low the first time it came on, never since, and the water level is still high.

 

pop your radiator cap when its dead cold and see where its sitting. if its a little low, top it off. all these new trucks seem to have nothing but problems. my 90 was leaking coolant out of both my heads and i never got a light or anything.