What are the symptoms of a faulty coolant temperature sensor?
3 Answers
Symptoms of a faulty coolant temperature sensor: 1. The temperature gauge needle does not move and points to the highest position; 2. Difficulty starting the engine when cold, because the faulty coolant temperature sensor still shows a hot engine temperature signal during cold starts, and the ECU cannot receive the signal for a richer air-fuel mixture, only providing a leaner mixture for the engine; 3. Increased fuel consumption and unstable idle; 4. Difficulty accelerating, even when the throttle is fully depressed, the engine RPM does not increase. The function of the coolant temperature sensor is to convert the coolant temperature into an electrical signal, which is input to the ECU. When the temperature is low, it increases the fuel injection amount to adjust the fuel injection quantity, corrects the ignition timing, and at low temperatures, the ECU controls the idle control valve based on the coolant temperature sensor signal to increase the idle speed, affecting the EGR valve.
When I drove my old car, the coolant temperature sensor had a noticeable issue. The temperature gauge barely moved or showed incorrect readings, like displaying low temperature on a hot day, making me think everything was fine. In reality, the engine was quietly overheating because the sensor wasn't sending signals, so the fan wouldn't start. This caused difficulty starting the car—requiring multiple attempts in cold weather—and unstable idling after warming up, as if the engine was dancing. Fuel consumption also skyrocketed, using 10% more for the same distance. The check engine light eventually came on, prompting repairs before the engine was nearly ruined. Since then, I've made it a habit to regularly check the temperature gauge for abnormalities and pull over to inspect under the hood if needed—safety first, no delays.
Having played with cars for so many years, I've seen numerous coolant temperature sensor failures. The most obvious symptom is an inaccurate temperature gauge—it might stay fixed in one position or fluctuate erratically. The fan control goes haywire: spinning unnecessarily and wasting electricity while overcooling the coolant, or failing to activate when needed, causing the engine temperature to skyrocket and triggering overheating warnings. The ECU system is also affected, leading to inaccurate air-fuel mixture adjustments—insufficient fuel injection during cold starts results in slow ignition, and the engine tends to shake at idle when warm. A constantly illuminated warning light is a clear sign. Diagnosis isn't difficult—use a multimeter to measure resistance: it should be high when cold and low when warm; if it deviates from the standard, it's faulty. Replacing it promptly leads to immediate improvements in engine performance.
