OBD Code PO128 Thermostat Question

[Cordts]

Is it at all possible that the thermostat is ok and the temp sensor on the upper radiator hose is bad?? The temp meter reads normal...

[drive-ability]

Here is the way I think it works,
Your computer expects the engine temp to rise at a given rate. With a working Thermostat the temp gain is predictable. I would think there are other inputs used to triangulate the thermostat's pass / fail outcome.
Bottom line is the engine should reach operating temp quickly in its usual way. If it takes longer for the engine to reach operating temp the code will trigger.
What does your temp gauge read after 5 minutes from a cold start ? Assuming you don't live in the north pole LOL

[LockDr816]

After warm up, feel the top and bottom radiator hoses. If the top one is considerably cooler than the bottom, the impellor in your water pump may be spinning freely on the shaft. Just had that problem on one of my father's cars.

[Cordts]

New thermostat assembly fixed the problem..