I had the same problem, literally. Wife called me telling me the low coolant level warning message kept coming up. Couldn't find the leak for the life of me but had obvious traces of coolant drops under the car. Even though I could see coolant running down the back side of the engine I couldn't pinpoint what the source was so I went to Autozone, put some dye in the expansion tank, went for a quick drive, and used a UV light to pinpoint it to one of the heater core hoses at the back of the engine.
