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The vehicle’s Temperature Sensors are components that play a very important role in the control of polluting emissions and fuel consumption. Their reading, together with that of other sensors, allows the control unit to parameterize the conditions of the injection system.
The vehicle’s Temperature Sensors are components that play a very important role in the control of polluting emissions and fuel consumption. Their reading, together with that of other sensors, allows the control unit to parameterize the conditions of the injection system.
Types of temperature sensors
There are different types of temperature sensors within the wide FAE range. They can be grouped into the following:
Its function is to measure the temperature of the engine coolant.
They are mounted in the cooling circuit conduit and their reading is sent directly to the control unit.
The operating temperature ranges from -40ºC to +130ºC.
This intake-air sensor records the intake air temperature, which can be used to calculate the intake air mass in conjunction with a boost pressure sensor. In addition, setpoints for control circuits (e.g. exhaust gas recirculation, boost pressure control) can be adapted to the air temperature.
The operating temperature range is from -40°C to +120°C.
Its function is to read the outside temperature of the vehicle. Like the other temperature sensors, the reading is sent to the control unit, where together with the reading of other sensors injection is managed.
Negative Temperature Coefficient thermistors (NTC thermistors) are resistors whose temperature coefficient is negative, i.e. the value of the resistance depends on the temperature. NTC thermistors are made from semiconducting metal oxides such as ferric oxide (Fe2O3) by substituting some of its iron ions by titanium.
For graphical representation we need to apply the following equation:
Positive Temperature Coefficient Thermistors (PTC) exhibit an increase in electrical resistance when subjected to an increase in body temperature.
The initial materials used are milled, mixed with ceramic additives, pressed into moulds and sintered. Its graphical linear representation, unlike the NTC, is to be found on below chart:
Features of temperature sensorsFAE sensors are based on a thermistor inserted at one end of a metal body, either cylindrical or hexagonal.
It is this end that comes into contact with the refrigerant (threaded or inserted directly into the cooling system of the vehicle) or with the air and will be responsible for displaying temperature and send the information to the ECU of the vehicle.
The connecting part of the sensors is usually made of plastic. It fits to the different connectors which cover the vast majority of vehicles on the market. A metal or rubber gasket ensures the tightness between the sensor and the engine block.
The metal body, connector and cables must be checked to ensure that they are in good condition.
Also check whether the sensor shows any cracks, dents or bumps that could have damaged it.
It should be noted that, as a general rule, a visual inspection is not sufficient to ensure that the part is working properly or not, but it helps to make an initial diagnosis.
The specific values of the sensors must be checked each maintenance or every 25.000km. Remember that refrigerant can cause corrosion and disable the res- ponse of the sensors. In case of air sensors the possibility exists that impurities obstruct the pipes which results in the impossibility of performing readings by the sensor. Replace the sensor whenever results are diagnosed which are not within the specified operating limits.
The torque of the sensor temperature is 30 ÷ 50Nm. Replace the gasket each time the sensor is changed. The gaskets do not perform their sealing function if these are used or worn.
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