I have a check engine light on for about a month now and am almost 100% sure it is the 02 sensor(s) because of the not so good fuel mileage. Car runs perfect though. My question is how do I know if it is the one on the front of the engine or the other one? Which is my second question where is the other one? I can see the first one right in front of the radiator but not the other. Thanks!!! :)Nelson