i took my car into pep boys yesterday because my car has been givin me the check engine light on and off for about a week. it will come on for about three day then go away. so i have them check it out and they get a code that says it is the cooling thermostat. so the guy tells me either it is the termostat or the sensor of engine temp. to get the thermostat replaced will cost about 180. to get a full diagnostic will cost 90. and he didnt mention anything about the sensor. anybody have any clue why the engine light would come on and off by itself over a few days?? and what would be the best way of going about getting it fixed?