What are the symptoms of a faulty coolant temperature sensor?

[LeCaroline]

The symptoms of a faulty coolant temperature sensor are: 1. The temperature gauge needle does not move and points to the highest position; 2. Difficulty starting the engine when cold, displaying a warm engine temperature signal, causing the ECU to receive no signal for a rich air-fuel mixture and only providing a lean mixture; 3. Increased fuel consumption and unstable idle; 4. Difficulty accelerating, with the engine speed not increasing even when the throttle is fully pressed. A sensor is an electronic component in the car's circuit. If it is damaged, there is little room for repair, and it must be replaced. If you want to test the sensor, a simple method is to place the coolant temperature sensor in a heating cup (be careful not to submerge the connector part) and use the "resistance range" of a multimeter to measure it. As the temperature rises, the resistance should decrease. If there is no change, it indicates that the sensor is faulty.

[SanSimon]

I remember when the coolant temperature sensor went bad, the car had a lot of issues. First, starting in the morning was particularly difficult, with cold starts being a struggle, and the engine seemed to be laboring. The temperature gauge would also act up, sometimes showing the lowest temperature even when the engine was already hot. The fan could go out of control, either running non-stop or not turning on at all, causing the engine temperature to rise rapidly. Idling became unstable, with the car shaking noticeably when parked. Fuel consumption also increased significantly because the computer wasn’t receiving the correct temperature signal, preventing the fuel injection system from optimizing. Additionally, the warning light on the dashboard would frequently come on, acting as an alert. If not repaired promptly, it could damage the engine, such as overheating and burning out the cylinder head. I recommend getting it checked at a professional repair shop with a diagnostic tool as soon as these issues are noticed—fixing small problems early can save a lot of money.

[VonBenjamin]

As a tech enthusiast, there are several typical symptoms of a faulty coolant temperature sensor. It measures the coolant temperature and sends feedback to the ECU. If it fails, incorrect sensor signals can cause the engine control module to malfunction. The most common issue is difficulty starting a cold engine, as the ECU misjudges the temperature and injects too much or too little fuel. Fan control also becomes erratic—running at high speed when it should be low or not running at all. The dashboard may display inaccurate low-temperature readings. At idle, the RPM fluctuates noticeably, causing the car to shake. Fuel consumption can increase by over 10% compared to normal, and engine performance declines. Long-term neglect may lead to more severe problems, such as piston overheating and deformation. Fortunately, modern cars have an OBD diagnostic port, allowing you to check trouble codes with a scanner. I often help friends inspect these issues to prevent bigger problems down the line.

[Damian]

There are many symptoms of a faulty coolant temperature sensor. I would notice the temperature gauge being inaccurate, with the needle indicating incorrect low temperatures. Starting the engine becomes difficult, especially on cold days when the car won't start. The fan may sometimes stop working or operate erratically, causing the engine to run too hot or too cold. A lit-up warning light on the dashboard is a common signal. Unstable idle speed makes the car shake at red lights. Fuel consumption may also increase slightly. If you notice these signs, get it checked as soon as possible—don't wait until the problem worsens.