How to Determine if the Coolant Temperature Sensor is Damaged?
3 Answers
Methods to determine if the coolant temperature sensor is damaged include: 1. The temperature gauge needle does not move or points to the highest position; 2. Difficulty starting the engine when cold; 3. The engine speed cannot increase even when the accelerator is fully pressed. Ways to test if the coolant temperature sensor is damaged are: 1. Use a hairdryer to heat the coolant temperature sensor and measure the resistance with a multimeter—no change in resistance indicates a damaged sensor; 2. Use a diagnostic tool to test the sensor when the engine is cold. The coolant temperature sensor is an electronic component in the car's electrical system. If it fails, it cannot be repaired and must be replaced. The functions of the coolant temperature sensor are: 1. Increasing fuel injection volume at low temperatures; 2. Delaying the ignition timing at high temperatures to prevent knocking; 3. Converting coolant temperature into an electrical signal and inputting it into the ECU.
Last time my car's temperature gauge wasn't moving at all, yet the electric fan was spinning wildly. Later diagnostics revealed an abnormal signal from the coolant temperature sensor. Common symptoms include difficulty during cold starts and lack of power when accelerating in a warmed-up car. Sensor failures come in two types: one is resistance drift causing inaccurate signals; the other is complete open or short circuit making the system default to extreme temperatures. If the ECU suddenly behaves normally after unplugging the connector, it's almost certain the sensor is faulty. Repair shops typically use two testing methods: measuring if the resistance value deviates from the 30-50 ohm range at room temperature, or boiling the sensor in water to observe resistance changes. A faulty sensor will also trigger a P0115 trouble code.
As an experienced auto mechanic, here are a few self-check tips for you: Feel the water pipe when starting a cold engine - if the engine is very hot but the temperature gauge shows the lowest reading, be alert. Fluctuating gauge readings are often early warning signs. Many modern vehicles have dual protection systems with both primary and emergency sensors. When the primary sensor fails, the system defaults to a fixed value, making the gauge appear normal while the engine shows obvious abnormalities. The most direct method is to check the data stream with a diagnostic tool - a normal coolant temperature curve should be continuous. If it suddenly drops from 80°C to 50°C, it indicates signal interruption.
