Hi, is there anyone can help me!?

Engine code P0046

Engine low coolant light used to turn on once every week so I put Liquid on expansion tank to block any leakage in system, It works , no further coolant loss but,

few days ago while i was driving "Engine restricted Performance" turned on follow by Amber Engine Light and and I could feel Engine performance decreased but

when I leave the vehicle for few hours off then drive again Power seems ok, and restricted message disappear, if I reset the code then engine light also disappear but

it will happen again (message and lights come on) after while driving!

anyone can help me?!