Mazda 3 GS-Sky 2014 51k engine light code P0126

Hi guys I was wondering if you could help me out. I got this engine light and code P0126 a few weeks ago. I brought it to my friend who’s a mechanic and had him look at it for me. He replaced the thermostat on it and topped up my coolant fluids and also said that there was nothing blocked in the line. The engine is lot over heating at all, seems to get up to heat at the same time as usual and I get heat out of my heated. My warranty of course just ran out a few months ago.. any advice would be greatly appreciated.