I think I may need help on this. I got this P0128 code the first time on my 2011 wrx sedan at 3000 miles. I had autozone reset it and it came back 300 miles later. It went away on its own after another few hundred miles, but came back shortly after.
I took it to the dealer and they flushed the radiator and the ecu was reset. The code was gone for a few thousand miles.
I took the car into the dealership again at 12000 miles with the same p0128 code. They changed out the thermostat and reset the ecu again.
I was fine until 15000 miles and the lights came on again. I decided to get a Cobb and exhaust and change the flash it to stage 1. This resolved the error code until 18000 miles. I uninstalled the Cobb stage 1 and took the car to the dealership.
They flashed the ecu with a new map that is suppose to be a fix for the p0128 code. I am now at 22500 miles and the p0128 code is back.
Has anyone else had this issue? Any suggestions on how to resolve this?