1998 Saturn station wagon.

It's a four door station wagon 1.9 liter I4 SFI engine, SW2. Engine service soon light comes on every month, or so. Local Garage unhooks the battery, reseting the code, & tells me my gas cap was loose. It stays off for another month, then comes on again. Also, right after starting to drive the car, a few minutes later, the two red coolant temp, & coolant level lights flash together (same bulb??), but the car runs fine. Then, they go off, & MAY come on again. Is it a faulty Engine Coolant Temperature Sensor? Dani