Description

Air Temperature Sensor Description
1. Fault Codes:
Intake Air Temperature Circuit Low Input P0112
Intake Air Temperature Circuit High Input P0113
Intake Air Temperature Sensor Rationality Check P0111

2. Monitoring Procedure

Range Check
Problems with the air temperature sensor are detected using a range test. The range test tests for input values outside expected limits. If the range tested is not passed then the appropriate fault count will be incremented, otherwise it will be decremented. If the count reaches a given threshold then a fault is present. While fault counting is in progress a back-up value of air temperature will be supplied to avoid the problems of incorrect values reaching the rest of the system.

Rationality Check
Once the engine coolant temperature has stabilized hot, the output of the air temperature sensor is compared at low and high airflow conditions. The test relies on the fact that the under bonnet temperature causes the air temperature to rise at idle compared to high airflow conditions, where the real external ambient temperature is being read. These tests will check that the sensor is correctly mounted and connected. The tests are two-sided, but only one flow chart and diagram have been shown.

3. Primary Detection Parameter
Air Temperature - measured as thermistor voltage.

4. Fault Criteria Limits
Intake Air Temperature Circuit Low Input 0.059V - equivalent to 145° C
Intake Air Temperature Circuit High Input 4.922V - equivalent to -40° C
Intake Air Temperature rise/fall during rationality check approx 3° C

5. Monitoring Conditions
The range check will take place whenever there is power to the ECM.
For the rationality check, the following conditions must be met in consecutive order:
I. engine coolant temperature is above a threshold (70�C).
II. engine operates at a constant air mass flow rate for a period of time.
III. the average air mass flow rate changes at a certain rate.
IV. engine maintains that new air mass flow rate for the period of time that the sensor output test is being conducted.
If any of the conditions fail to be true, the test is restarted.

6. Monitoring Time Length / Frequency of Checks
The frequency of the Air Thermistor Diagnostic is 2Hz. The rationality check will take place at least once per trip.

7. Criteria for Storing Fault Code
Two successive trips where the air thermistor diagnostic indicates a failed air temperature sensor.

8. Criteria for Illuminating MIL
Two successive trips where the air thermistor diagnostic indicates a failed air temperature sensor.

9. Criteria for Determining Out of Range Input Signals
Range check as above.