I just bought my car a month ago with 50000 miles, and the check engine light came on a couple days ago. I took it to the shop and they told me there was insufficient engine coolant temperature. Take it straight back to the dealership. The temperature gauge keeps reading cold, then hot, then normal. Constantly fluctuating. My car is covered under a 90 day power trane warranty so it may or may not be covered. I'm worried something serious is wrong. Do you have Any input?