1 1/2 years ago had coolant temp. Sensor replaced when the " check engine light" came on, my mechanic checked the codes and said this was the problem. 3 months ago the " check engine light" came back on and also the temperature guage would act very strange, it would sometimes operate in the normal range on the guage and other times hardly move at all on the guage, also sometimes the heater would throw hot air and other times just luke warm air even when on the hootest setting. My mechanic, again checked the code and again the same remedy was performed. Yesterday the dumb " check engine light came on again, and also the temp. Guage doesn't move off the lowest setting, and also the air is only luke warm at the highest setting. Checked antifreeze level and everything is full. Any suggestion would be appreciated. This is a 2.0 liter engine with about 79000 miles on it.