How to Determine if the Coolant Temperature Sensor is Faulty?

[BrynleeFitz]

Here are the methods to determine if the coolant temperature sensor is damaged: 1. The temperature gauge needle does not move or points to the highest position. 2. Difficulty starting the engine when cold, because a faulty coolant temperature sensor still shows the temperature signal of a hot engine during cold starts. The ECU cannot receive the signal for a rich air-fuel mixture and can only provide the engine with a leaner mixture. 3. Increased fuel consumption, unstable idle; difficulty accelerating, even when the throttle is fully pressed, the engine speed does not increase. Here is some relevant information: 1. When the coolant temperature sensor fails, it often still shows the temperature signal of a hot engine during cold starts. The ECU cannot receive the signal to provide a rich air-fuel mixture and can only supply the engine with a leaner mixture (the signal for a hot engine), making it difficult to start the engine when cold. 2. Most automotive coolant temperature sensors are made using NTC thermistors. The engine control unit (ECU) receives the resistance value transmitted by the NTC. For the ECU, the received signal is either a resistance of 0 or an infinite resistance.

[LaNaomi]

I've been driving for over ten years and have encountered cases of faulty coolant temperature sensors a few times. It's not difficult to identify. If the temperature gauge needle constantly stays at the lowest position or jumps around inaccurately, it's likely the sensor is faulty. I remember once when I was driving, the engine started overheating and smoking, but the fan wasn't running—turned out to be a sensor failure. Simple diagnostic methods: First, observe the dashboard. The coolant temperature should gradually rise during a cold engine start. If there's no movement or erratic changes, it's suspicious. Then, plug in an OBD scanner to check if the trouble codes show coolant temperature-related errors, such as P0115. If you don't have a tool, try unplugging the sensor connector after parking—if the fan spins wildly, it indicates control malfunction. If this part fails, replace it promptly; otherwise, the engine may overheat and be ruined, leading to expensive repairs. During routine maintenance, check the sensor connector and keep it clean.