The Intake Air Temperature (IAT) is a thermistor built into the air flow meter or is mounted on the air cleaner housing. A thermistor is a resistor which changes resistance value based intake air temperature. Low manifold air temperature produces a high resistance: 100,000 ohms at -40°F (-40°C). High temperature cause low resistance: 70 ohms at 284°F (140°C).
The ECM supplies a 5 volt signal to the IAT sensor through a resistor in the ECM and monitors the voltage. The voltage will be high when the manifold air is cold and low when the air is hot. By monitoring the voltage, the ECM calculates the air temperature and uses this data to help determine the fuel delivery and spark advance.
See Figures 1 and 2
- With the IAT sensor exposed, measure the resistance between terminals E2 and THA of the air flow meter or the IAT sensor itself, with an ohmmeter. Check the ambient air temperature with a thermometer. Compare the resistance with the temperature as per the graph. Using a hair dryer, warm the air around the sensor and check the resistance once again.
- If it sensor does not come within specifications, replace the sensor. If the sensor is contained inside the air flow meter, the entire unit must be replaced.
REMOVAL & INSTALLATION
This applies only for sensors mounted on the air cleaner housing.
- Detach the electrical harness.
- Unscrew the sensor and remove it from the housing.
- Install the sensor into the housing.
- Attach the harness.