This coolant temperature sensor monitors the engine coolant temperature and sends a signal to the engine control unit. The ECU uses this signal to adjust fuel injection timing, injection quantity, and the radiator fan engagement point. A failed sensor typically causes the ECU to default to a fixed temperature value, which can result in poor cold-start behavior, increased exhaust emissions, or the radiator fan running continuously. The sensor threads into the engine block or thermostat housing and uses a sealed electrical connector. On reinstallation, ensure the sealing washer is replaced and the sensor is torqued to specification to prevent coolant leakage.