When the water temperature sensor malfunctions, the temperature signal displayed when starting a cold car is often the same as when starting a hot car. The ECU cannot receive a signal to provide a rich mixture, and can only supply the engine with a thinner mixture (the signal when starting a hot car), making it difficult to start a cold car. In this situation, it is necessary to check whether the contact of the water temperature sensor plug is normal or replace the water temperature sensor.

For example, when reading the static engine data of the car (referring to when the car is cold), it is found that the coolant temperature output by the engine ECU is 105 ℃, while the actual temperature of the engine at this time (set to winter temperature) is only 1 ℃. It is obvious that the water temperature signal received by the engine ECU is incorrect, indicating that there is a problem with the water temperature sensor.
It should be noted that sensors are electronic components in automotive circuits. If this component is damaged, there is not much room for repair, and only replacement is necessary. If you want to test it, a simple method is to place the water temperature sensor in a heating cup and heat it (be careful not to submerge the plug part). Use the "resistance gear" of a multimeter to measure. When the temperature rises, the resistance should decrease. If there is no change, it indicates that the thing is broken.

If using a diagnostic tool to test this component, it is necessary to test it when the car is cold.
The function of the water temperature sensor is to convert the cooling water temperature into an electrical signal, which is input into the ECU and includes: 1. Correct fuel injection quantity; Increase the fuel injection rate when the temperature is low. 2. Correct ignition advance angle; Increase the ignition advance angle at low temperatures, and delay it at high temperatures to prevent detonation. 3. Affects the idle control valve; At low temperatures, the ECU controls the action of the idle control valve based on the water temperature sensing signal to increase the speed.