Ok on the way home from work today I got the famous P0128 code. I read up and everyone says thermostat. But my question is that u have the had the trailblazer for about a year and always had my scan gauge hooked up to it an it had always read 184 degrees and the guage has always been just a hair under 210. Well on the way home today when the check engine light came on it read the same thing the whole time. And I just filled the trailblazer up Friday and got 19 mpg (not to bad). I had just changed the plugs so I thought maybe that was te reason for the light but I guess not. I turned the light off with the scan guage to see if it will come back on but are you guys sure that it is the thermostat? Any other ideas?