Hey everyone, Ive been having a problem with my 03 Envoy that I haven't been able to figure out as of yet. So far my code on my car reads as P0128, and it has read this for about a year. I have replaced the thermostat on my car which i thought would fix the problem but it hasn't gone away. So i figured it might be a temp sensor reading incorrectly causing the light to come on, i replaced this also but to no avail. The light still comes on and reads P0128. My temp runs below 210 which is the normal so im not sure what it is. The car heats up great in the winter and Ive owned an 02 Trailblazer and it heats up about the same so im inclined not to think i have another bad thermostat so i don't know what could be the problem. Any ideas?