Code PO128 on 2005 Chevrolet Trailblazer

I replaced the coolant temp sensor. I am still getting a PO128 code. I tested the sensor and it tests good. The gauge reads 200. What else could be causing the code?

Asked by for the 2005 Chevrolet Trailblazer
Did you replace the thermostat as suggested before? You say temp. reads 200 but is it constant while driving down the road? Unless you have a REAL scanner a DVOM and the savvy to use them, get a mechanic to have a look. Circuit or ecm problem, will have to be tested.
I have same problem. Always get same code. Now have intermittent starting problems and no mechanic around can seem to find the problem.