What Are the Common Faults of the Coolant Temperature Sensor?
3 Answers
Common faults of the coolant temperature sensor include: 1. Changes in thermistor performance; 2. Poor line contact or open circuit; 3. No coolant temperature signal or inaccurate signal from the ECU; 4. The cooling fan does not rotate; 5. The temperature gauge does not indicate. Methods to determine if the coolant temperature sensor is damaged are: 1. Use a digital resistance simulator to simulate the coolant temperature and compare it with the actual situation; 2. Use an infrared thermometer to test the actual temperature of the coolant sensor and compare it with the temperature gauge. The functions of the coolant temperature sensor are: 1. To drive the change of the temperature gauge by altering the current passing through the sensor via changes in internal resistance, indirectly reflecting the engine's operating temperature; 2. To provide the engine control unit with an analog signal of temperature changes.
Over the years of car repairs, the most common issue I've seen is water temperature sensor connectors leaking and rusting. Coolant creeps up along the wiring harness, and once the copper terminals corrode, the signal gets distorted. As a result, the temperature gauge needle either jumps erratically or stops working altogether. There are plenty of cases where the engine seized because the instrument cluster showed 70℃ while the overflow tank was visibly steaming. Once, while dealing with a recurring overheating issue on an old Camry, I disassembled the sensor and found its ceramic resistor cracked into three pieces. After replacing it, the fuel consumption even dropped by 0.5L/100km. I also applied anti-rust grease to the wiring harness connector – five years later, the owner came back specifically to thank me for that.
I got hit by this issue last month! That day, the coolant temperature gauge on the dashboard suddenly dropped to the lowest point and stopped moving, and the AC stubbornly refused to blow hot air. The mechanic used a diagnostic tool and read the P0116 fault code, saying the sensor data was unreasonable. Upon disassembly, they found a crack in the sensor's plastic casing, and coolant had seeped into the electronic components. Replacing it with an OEM part cost me 380 yuan. The mechanic warned that continuing to drive could trigger the engine protection mode, leading directly to speed limitation. Now I've learned my lesson—every year when changing the coolant, I have them use an air gun to blow away dust and debris around the sensor.
