I have an '05 with 70k miles. Sometimes when it is cold out (40F or less usually) I've noticed my temperature gauge will suddenly drop down to zero, the check engine light comes on, and the radiator fans start running at all times. If i turn off the car and turn it back on it again, the temperature gauge comes back up as normally, and after 100 miles or so the check engine light turns off. This phenomenon happens quite often. Any ideas of what it could be? I'm guessing a bad sensor of some type... Thanks!