To determine whether your coolant temperature sensor is faulty, watch out for symptoms such as black smoke coming from the exhaust pipe, the engine overheating frequently and the car using more gas than it normally does. The car may also have a problem starting up after reaching its normal operating temperature. A defective coolant temperature sensor needs replacement.
The coolant temperature sensor is usually located close to the thermostat housing in the intake manifold or in the cylinder head. Depending on the vehicle, the coolant temperature sensor may be accompanied by a coolant temperature sending unit, which sends information from the control unit to the dashboard. The tip of the sensor should be in direct contact with the coolant so that it can read accurately.
Inspect the sensor for faults such as corrosion, cracks and leaks. If it has no visible faults, measure its resistance and voltage readings using a standard ohmmeter or a digital volt ohmmeter; the resistance value should increase as the sensor temperature decreases. If the sensor reads out of range, it needs replacement.
When replacing the sensor, ensure you first drain the coolant to a level that is below the sensor. Refill the engine with the coolant after replacing the sensor. Ensure there is no air on the cooling system as it causes the sensor to read incorrectly.