Air Temperature Sensor (ATS)

INTAKE AIR TEMPERATURE SENSOR (IAT)

ATS - AIR TEMPERATURE SENSOR

General description 
      ATS is a two-wire thermistor and measures the temperature in the intake manifold. The air density is inversely proportional to temperature. Thus the ATS signal provides more accurate engine sucked air mass calculation. 

Appearance 
Fig. 1 shows a typical ATS sensor.

Fig. 1

Principle of operation of the ATS sensor
      Reference voltage of +5V is applied to the sensor in open circuit and grounding is through the sensor’s feedback. Air temperature variable voltage is fed to the onboard controller. 
ATS location is important for the temperature range. According to the structural characteristics of the vehicle, ATS may be located in different locations:

• In the intake manifold;
• In the air filter box;
• Inside the MAF.

      Air temperature signal varies significantly from cold and hot engine start and from the ATS location. If ATS is in the intake manifold or in the air filter box, measured temperature will be engine bay dependable with range of 20ºС to 40ºС. If it’s located in the intake manifold or on the throttle body (in some SPi systems), temperature range can be much higher reaching 70ºС when engine hot. Some cars use two sensors – first measures the engine bay temperature and second measures the ambient temperature. This is especially useful if the car is turbocharged.

Used types of sensors 
      In most cases a negative temperature coefficient ATS sensors are used. But in some Renix systems sensors with a positive temperature coefficient can be seen.

Order to verify functionality of the ATS sensor

—Negative temperature coefficient ATS sensor— 
The NTC ATS sensor reduces its resistance with temperature increasing. 
ATS sensor can be located inside the MAF body or in the intake manifold. 
If it’s inside the MAF, it uses same ground wire as the MAF sensor.
Both are two-wire sensors and the verification operations are similar.

• Connect the negative voltmeter terminal to the chassis ground.
• Determine the signal and the ground terminals.
• Connect the positive voltmeter’s probe to the sensor signal wire. (ATS is located in the air filter box).
• Turn the ignition on but do not start the engine.
• Voltage value must be in the range between 2V to 3V depending on the temperature. Typical values of the voltage for different temperatures can be found in the ATS graduated tables.
• Voltage will change in accordance with the air temperature inside the intake manifold. When the engine bay or the manifold temperature increases, voltage decreases. When engine is cold, air temperature corresponds to the ambient temperature. After the engine start engine bay and manifold temperatures are rising and the manifold temperature could rise to 70ºC¸80ºC, which significantly exceeds that of the engine bay.
• If measurements have to be taken at different temperatures, ATS can be heated with air drier or cooled with a spray cooler. Heating and cooling the sensor will change its resistance and voltage too.
• Check whether sensor’s output voltage corresponds to its temperature.  Thermometer is needed.
• Warm the engine to operating temperature. Output voltage should decrease with the temperature increasing in accordance to the values in Table 1.

-- If e zero voltage is measured at the signal terminal, following steps have to be executed:

• Check whether the signal terminal is not connected to the ground.
• Check the wires between the sensor and the onboard controller for breaks.
• If the wires are good but still there is no output voltage, all power supply and ground terminals of the onboard controller must be checked. If there are correct, the onboard controller itself may be damaged.

-- If voltage of 5V is measured at the signal terminal, following steps have to be executed:

• ATS of MAF connector make bad electrical contact;
• Sensor circuit is broken;
• Sensor ground connection is broken.

-- If battery voltage is measured at the signal terminal or at the power supply terminal, checks for short circuit to the positive battery terminal and/or the power supply wire have to be executed. 

Oscilloscope measurements

• Connect the active oscilloscope probe to the sensor signal terminal and the ground probe – to the chassis ground.
• Switch the oscilloscope in continues measurement mode (detect slowly changing signals.
• Sink the sensor in a suitable water container that is heated.
• After several minutes of measurement, you’ll be able to observe the voltage change curve during the water heating (фиг. 2). Note the time of measurement - it is about 10 minutes.
• It is desirable to continuously take measurements of the heating water and compare them to the values in Table 1.

Fig. 2

— Positive temperature coefficient ATS sensor — 
      The PTC ATS sensor increases its resistance with temperature increasing (mainly in Renault cars). 
Generally verification is very similar to that of the NTC ATS sensor, described above. Results can be compared to that in Table 2.