pavich...just noticed this thread. Do you have atx or mtx? If you put PO128 into search engine (use capitals for PO) you'll find a few discussions on this CEL which only a few of us had back in '04, '05, '06. Happened mainly to '04 2.3 ATX owners. Had nothing to do with thermostat. I had my computer updated in feb '06 and both my gas mileage and heater improved. The problem was the coolant temperature sensor was reading the coolant as cold when it was actually warm. The update fixed it. Are you getting lousy mpg and poor performance from your heater?