Toyota Camry P0128

Hello again Car Talk folks.
I still have my 2001 Camry 4 cylinder and it is going strong with only 134,000 miles. Check engine light gives code P0128. I have noticed that the dash temperature gauge reads slightly lower than it usually does when the engine is hot.
Should I replace the coolant temperature sensor first?
Do I need a genuine Toyota sensor?
Would the thermostat have been replaced when I had the timing belt and water pump done about 3 years ago?
Or do I replace it only if a new coolant temp sensor does not fix the problem?

This code is usually caused by a thermostat that’s stuck partially open

Replace the thermostat.


Should I do the CT sensor as well, or just the thermostat? Thank you, Tester.

Just replace the thermostat.