* Inaccurate temperature gauge reading: This is the most obvious sign. The gauge might show a consistently incorrect temperature, either running too hot or too cold, regardless of the engine's actual temperature. It might even fluctuate wildly.
* Poor engine performance: The engine control module (ECM) relies on the temperature sensor's input to adjust fuel mixture and ignition timing. A bad sensor can lead to:
* Rough idling: The engine may idle poorly or stall.
* Hesitation or stumbling: The engine might hesitate or stumble during acceleration.
* Reduced power: You might notice a loss of power or sluggish acceleration.
* Poor fuel economy: The inaccurate fuel mixture can lead to significantly lower gas mileage.
* Check Engine Light (CEL): The ECM will likely illuminate the CEL and store a diagnostic trouble code (DTC) related to the coolant temperature sensor. You'll need a code reader to identify the specific code.
* Overheating (less common, but serious): If the sensor is faulty and reports a falsely *low* temperature, the engine could overheat because the cooling system isn't being regulated properly. This is a serious issue that could cause significant engine damage.
* Engine won't start (rare): In some cases, a completely failed sensor might prevent the engine from starting, particularly in cold weather.
It's important to note that some of these symptoms could be caused by other issues, so it's crucial to get a proper diagnosis from a mechanic or use an OBD-II scanner to check for diagnostic trouble codes before replacing the temperature sensor. Replacing the sensor is relatively inexpensive, but misdiagnosis can lead to more costly repairs.
