P0128 2005 Nissan Altima Sedan -

Question

WHAT IS THE NECESSARY PART TO REPLACE THIS MALFUNCTION AS THERE ARE MULTIPLE PIECES TO THE PUZZLE, ONE BEING TWO SIMILAR BUT DIFFERENT THERMOSTATS WITH SEPARATE FUNCTIONS.

Answer 1

if there is no coolant leaks, and your fans are working, replacing the thermostat is the first step (coolant temp sensor is second)

 

The thermostat is the red circle in picture below

there is a second one called a water control valve but it probably wont need replacing.