Automotive Mechanic Training - Car Repair and Maintenance - What is Engine Temperature Sensor? How Engine Coolant Temperature Sensor Works

What is Engine Temperature Sensor? How Engine Coolant Temperature Sensor Works The engine temperature sensor informs the engine’s ECU about the current & ongoing variations in the engine temperature. ECU, in turn, adjusts and regulates the fuel quantity & ignition timing. The data from the engine temperature sensor provides readings for engine temperature gauge on the dashboard. Based on this data, the ECU also controls the additional functions such as switching on / off the engine cooling fan. Engine Coolant Temperature sensor is primarily located in the coolant passage of the liquid cooled engine; typically near the thermostat valve. The engine temperature sensor connects either to the temperature gauge or to the temperature indicator in the dashboard. In modern cars, you will notice that there is no separate engine temperature gauge. Instead, there is a tiny ‘light’ symbolizing the engine temperature; which is integrated with rpm-meter. Upon turning the ignition 'ON', the letter ‘C’ also lights along with the temperature symbol; indicating that the engine is cold. It should automatically disappear; once the engine warms up to its optimum temperature (usually within 2/3 Kilometers of the drive). In most cases, the engine temperature sensor fails due to corrosion. This is because of its exposure to engine coolant. It may also fail if the coolant leaks through its wiring connector. If you see that the engine temperature symbol ‘C’ is lit continuously and does not disappear after some time; it indicates that there is some problem in the engine’s cooling system. Also, if the engine temperature goes above the prescribed levels (usually above 100o C), another symbol – a High-Temperature indicator light ‘H’ lights up in red color; indicating that the engine is over-heating. Because temperature plays such a vital role in engine performance calculations, any problem with the coolant temperature sensor can quickly translate into an engine performance issues. Usually a problem with the coolant temperature sensor will cause a few symptoms that alert the driver of a potential problem that should be thoroughly inspected. 1. Poor fuel economy One of the first symptoms associated with a problem with the coolant temperature sensor is poor fuel economy. If the coolant temperature sensor goes bad it can send a false signal to the computer and throw off the fuel and timing calculations. It is not uncommon for the coolant temperature sensor to fail and send a permanently cold signal to the computer. This will cause the computer to think the engine is cold, even when it is not, and as a result will use more fuel than necessary. This will reduce fuel economy, and may hinder engine performance. 2. Black smoke from engine Another symptom of a possible problem with the coolant temperature sensor is black smoke from the vehicle’s exhaust. If the coolant temperature sensor fails and sends a cold signal to the computer, this can confuse the computer and cause it to unnecessarily enrich the fuel mixture. If the fuel mixture becomes excessively rich to the point where the fuel cannot be adequately burned in the combustion chamber, it will burn up in the exhaust pipes and cause black smoke. In severe cases, the black smoke may be considerable enough to warrant not driving the vehicle. 3. Overheating engine Another symptom of a problem with the coolant temperature sensor is an overheating engine. The coolant temperature sensor can also fail in a manner that causes it to send a permanently hot signal. This can cause the computer to incorrectly compensate for a lean signal, which can result in overheating, and even misfires or engine ping. 4. Check Engine Light comes on An illuminated Check Engine Light is another symptom of a potential problem with the coolant temperature sensor. For some vehicles the computer will set off a Check Engine Light if it detects a problem with the sensor’s signal or circuit. The Check Engine Light will remain on until the issue is addressed. Furthermore, it is not safe to drive a car with the indicator light ‘H’ on. As it may cause further damage and/or seize the engine. Stop the car and look for any coolant (usually green colored) leakage. If there is a noticeable leakage, do not drive the car in that condition. Instead, tow it to the nearest service station for repair.