How to Determine if the Coolant Temperature Sensor is Faulty?
3 Answers
If the diagnostic tool displays a fault code for the coolant temperature sensor, it indicates that the sensor is faulty. However, it is important to note that the inspection should be performed when the engine is cold. Use a multimeter to test the sensor, and then heat the coolant temperature sensor with a hair dryer. If the resistance value does not change, it means the coolant temperature sensor is already damaged.
Last time my car's temperature gauge was fluctuating, so I went straight to my friend's repair shop for a check. The experienced mechanic told me to start the engine cold first and observe if the temperature gauge showed normal low temperature; after the car warmed up, the needle should stabilize in the middle range. If it always showed low temperature or suddenly spiked to the red line, it was most likely a sensor issue. He used a diagnostic tool to detect fault code P0118, and the data stream showed erratic temperature readings, while the actual radiator temperature felt normal. Later, he removed the sensor and tested its resistance in warm water, finding that the resistance didn't change with temperature, confirming it was faulty. The mechanic said a faulty sensor could also cause a spike in fuel consumption because the engine control unit would mistakenly increase fuel injection.
Recently, the temperature gauge needle on my car's dashboard got stuck at the lowest position and wouldn't rise even after driving for half an hour. Checking the manual revealed that a faulty coolant temperature sensor often exhibits three symptoms: complete failure of the temperature gauge, illumination of the engine warning light, and abnormal difficulty during cold starts. At the repair shop, the mechanic first used a multimeter to test the circuit voltage. After unplugging the sensor connector, he could still measure a 5V reference voltage, indicating the wiring was fine. Then, he poured hot water over the sensor housing to simulate temperature rise, but the multimeter showed no change in resistance, confirming the sensing element had failed. He mentioned this part only costs around a hundred bucks, but if damaged, it could cause the fan to run excessively or stop working entirely.
