XJ-8L Sedan (X308) V8-4.0L (AJ27) (2001)
Intake Air Temperature Sensor: Description and Operation
Intake Air Temperature Sensor
Intake Air Temperature Sensor
The IAT sensor is a thermistor device mounted inside the MAF sensor. It provides an input signal to the ECM proportional to the temperature of air
passing through the inlet duct into the engine. A DTC is recorded if the voltage input signal from the sensor to the ECM is outside pre-defined thresholds
at the high or low end of the scale.
High/Low Input Failure
These are continuous monitors. The voltage from the sensor is compared to a failure threshold defined in the software. If the voltage is below the low
threshold, then a timer starts to increment. Once this timer exceeds another threshold, then a failure flag is set and a DTC is stored. If the voltage is over
the high threshold defined in the software, then a timer starts to increment. Once this timer exceeds a threshold, then a failure flag is set and a DTC is
stored.
Range/Performance Check 1
If engine speed and intake airflow is sufficient, the ECT is low enough and the air temperature sensor voltage is lower than calibrated constants, then a
monitoring failure judgment is made.
If after a calibrated period has elapsed the voltage from the sensor is greater than a calibration constant then a monitoring normal judgment is made.
Range/Performance Check 2
At intervals of approximately 2 seconds, the IAT is sampled to monitor for rapid drop in air temperature. If the change in IAT (over a 6 second period)
is greater than a calibration constant then a monitoring failure judgment will be made. A normal judgment is made if the change in IAT change is less
than this calibrated value.