Intake air temperature sensor - How It Works

General points

The intake air temperature sensor determines the temperature in the intake pipe and sends the voltage signals produced by the effect of temperature to the control unit. This evaluates the signals and influences the fuel induction and the ignition angle.

Function

The resistance of the temperature sensor changes depending on the intake air temperature. As the temperature increases the resistance decreases – and with it the voltage at the sensor. The control unit evaluates these voltage values, since they are in direct relation to the intake air temperature (low temperatures result in high voltage values at the sensor and high temperatures in low voltage values). 

Effects of failure

A faulty intake air temperature sensor can become noticeable in different ways through the fault recognition of the control unit and the resulting limp-home running strategy. Frequent fault symptoms are: 

■ Storing of a fault code and possible lighting up of the engine warning light 

■ Start-up problems 

■ Reduced engine performance 

■ Increased fuel consumption 

There can be a number of reasons for sensor failure: 

■ Internal short-circuits 

■ Interrupted cables 

■ Cable short-circuit 

■ Mechanical damage 

■ Soiled sensor tip

Troubleshooting

■ Read out the fault code 

■Check electrical connections of the sensor cables, the connector and the sensor for correct connection, breaks and corrosion

Testing takes place using the multimeter

1. 1st test step 

The internal resistance of the sensor is determined. The resistance depends on temperature: when the engine is cold, resistance is high and when the engine is warm, resistance is low. Depending on the manufacturer: 25 °C 2,0 – 5,0 KOhm 80 °C 300 – 700 Ohm Note special reference value specifications.

2.  2nd test step

Check the wiring to the control unit by checking every single wire to the control unit connector for transmission and connection to ground.

1. Connect the ohmmeter between the temperature sensor connector and the removed control unit connector. Ref. value: approx. 0 ohm (circuit diagram necessary for pin allocation on the control unit).

2. Use the ohmmeter to test the respective pin at the sensor connector and removed control unit connector to ground. Ref. value: >30 MOhm.

3. 3rd test step

Use the voltmeter to test the supply voltage at the removed sensor connector. This takes place with the control unit inserted and the ignition switched on. Ref. value: approx. 5 V. If the voltage value is not reached, the supply voltage of the control unit including ground supply must be checked against the circuit diagram. If this is OK, a faulty control unit must be considered.