OK I flipped over printer and checked all connection to the stock mainboard. I checked with continuity meter to see wires are good to heater, they were good. I then ran nozzle temp alone up to 150, that was good. Then 160, that was good. Then I tried 180 and around 168 the message popped up again. GRRRR

Ender 3 Pro
Ender Extender 300XL ( 300x300 bed) Mirror bed
120 volt 750W heater, SSR, and insulation blanket
Dual Z screws
All metal extruder
NEW 1k Thermister I thought that had gone bad(original 2+years old) Nope not cause