P0126 Mazda - Already replaced thermostat last year could it be the thermastat again?

Question

I replaced the thermostat about 1 year ago. Could it be the thermostat again. Plus how do I check the coolant level sensor.

Answer 1

It can be the thermostat again, most likely it is stuck open if your car has not overheated. 

or the coolant temp sensor 

see picture below