9 out of 10 times it's the thermostat.........
The code sets because of the amount of time it takes for the vehicle to get to normal operating temp......if the time is too long or does not reach the set temp, then the PCM turns the CE light on.....this happens because the therm is slightly open and allows too much flow through it....
Yes you will feel heat, and think the thermostat is ok.......vehicle is just not getting to normal temp on time, or it drops below this set temp while driving down the road, and does not get back to the set temp in a certain amount of time....
When ever I get one of these codes, I attach my scan tool, and let the vehicle idle until reaching normal operating temp, 190F+......
Then I go down the highway, and observe coolant temp data......if you see coolant temp dropping below 180F or more, replace the thermostat and clear the code...this will happen because the airflow through the radiator will cool down the coolant because of the bad therm.......stop and idle the car and it will eventually get back up to temp.....replace the thermostat....