IAT sensors sense the air temperature on the inlet side of the engine. The voltage signal, produced by the sensor, is passed to the ECU. The ECU evaluates the signal and influences the fuel injection timing and ignition timing.
Depending on the inlet temperature the resistor of the IAT changes. If the temperature rises up the sensor is reduces the voltage of the sensor. The ECU assesses the voltage value because it is in direct relation to the inlet air temperature. That means low temperature high voltage, high temperature low voltage.
Effects of failure
A faulty IAT can be noticed through:
- engine warning light illumination
- hard starting
- less engine power
- higher fuel consumption
- fault code present
Causes of failure
- mechanical damage
- wire short-circuit/open circuit
- internal short-circuit
- sensor tip soiled
For fault recognition consider the following system tests:
- read out fault codes
- electrical leads checked for correct fitting and contact
Use a Multimeter to check.
1. Find out the internal resistance. It is dependent on the temperature, cold engine high ohm, hot engine low ohm. According to the manufacturer:
2.0 – 5.0 Kohm
300 – 700ohm
Note the set point specification.
2. Wiring harness to the ECU plug, check for continuity and short-circuit to earth.
- Measurement with a ohmmeter between sensor plug and removed ECU plug, measured value: < 1 Ohm (circuit diagram needed for pin definition)
Respective pin from the sensor plug checked for short-circuit to earth, ECU plug removed, measured value: >30 MOhm
3. Measurement with a voltmeter on the sensor plug, checking the supply voltage. ECU plug fitted, ignition on, measured value approximately 5 V. If the voltage is not enough check the operation voltage and the ground of the ECU(circuit diagram needed).