Coolant temperature sensors send your engine's coolant temperature to the ECU. The ECU decides when the vehicle has warmed up after starting and adjusts the fuel curve to compensate for engine temperature. It also sends that information to your dash display, letting you know if your vehicle is overheating

If this piece fails, you will have no heads up display for coolant temperatures and you can experience poor performance. Hard idling, rough starts, and poor warm engine performance are all symptoms of a failed sensor. Replace yours for a low cost and keep your vehicle from running too rich and wasting gas.