Temperature Sensor

Temperature sensors used for engine control include coolant temperature sensor, intake air temperature sensor, and oil temperature sensor. Most of them are NTC thermistor type sensors. As to NTC output of the thermistor, resistance decreases with increasing temperature.
The measuring temperature range and characteristic vary depending on constituting substances of thermistor.

• Coolant temperature sensor is installed for thermistor part to contact with flowing coolant at cylinder block water jacket.


• Intake air temperature sensor is installed at surge tank, with the thermistor part of the sensor contacting with intake air. As these two sensors (IAT & MAP) are installed at the same part and have functionally associated with each other, they are sometimes integrated together and installed as a part.

ECU provides 5V supply voltage to sensor part via internal resistance. Then on the basis of sensor resistance value, signal voltage will rise with lower temperature and drop with higher temperature. ECU detects this voltage value for calculating temperature. Checking Intake Air Temperature Sensor
The Input voltage of 5V is provided to terminal B and resistance R is installed inside ECM.
When using volt-meter, turn on terminal ignition switch and measure the voltage, and then compare with specified value. As NTC thermistor type is used, higher temperature will reduce output voltage. Otherwise disconnect connector and check if supply voltage of 5V is operating normally at harness side. In addition check for circuit break and short.
And you can do the same for checking the Coolant Temperature Sensor.

• For troubleshooting of intake temperature sensor, resistance value and output voltage change by temperature variation are used for diagnosis. And connector connection and break and short shall be checked as well.


• For checking a separate part, use similar device generating hot air (ex. Hair dryer, etc) to measure resistance value and output voltage change by temperature variation.
  Then if resistance value does not change by temperature variation, it will indicate sensor failure. Replace the sensor.

Intake temperature sensor:

• Ignition timing correction may be impossible and generate knocking.


• Acceleration is poor during running.


• Higher fuel consumption.

Coolant Temperature Sensor:

• Poor start-up and engine malfunction during idling after start-up.


• Sudden engine stop during idling or running.


• Higher fuel consumption and higher emission of CO and HC.

You can check the sensor actual value and status by AutoHex auto Diagnostic Scanner under the supported car brand and according to engine type.

AutoHex II

Autohex II For BMW

AutoHex II For Kia and Hyundai

AutoHex stand alone

Mercedes Technical Info