P0126 Mazda - How do I know if it's the Thermostat or Sensor

Question

Recently had the P0126 code on my 2006 Mzda3s with 180k miles. From what I can tell, I either need to replace the thermostat or the sensor. How am I to know which one to replace? I have seen something about temperatures and how quickly they should be reached but how do I check that?

Answer 1

With 180k I would replace the both. They are not expensive at all. 

 

if you are going to install it yourself here is the instructions below