P0455 is not related to the engine coolant. It indicates a leak in the evaporative emissions system. It could be a hose disconnected or damaged, a valve stuck, or a loose gas cap.
There is a hose from the top of the expansion chamber that is the overflow, and is the only one that is not connected at both ends. If your system is over-filled coolant will spill out of that hose when the engine gets hot. Check the level when the engine is cold, and it should be at or slightly below the seam in the middle of the expansion tank. If you fill the tank above that when the engine is cold it will overflow when it is hot.
NEVER open the tank cap when the engine is hot. ALWAYS wait for it to cool down.
If you are getting a low coolant light there is a leak somewhere, and a common place for that leak is the water pump. If that is leaking you will have to replace it.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked