3.10 Intake Air Temperature Sensor
3.10.1 Description
1. Diagnostic Trouble 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 intake air temperature sensor are detected usin
g a range test. The range test tests for input values outside
expected limits. If the
range tested is not passed then the appropr
iate fault count will be incremented, otherwi
se it will be decremented. If the count
er reaches a given
threshold then a fault is present. While f
ault counting is in progress a back-up value
of intake air temper
ature will be suppli
ed to avoid problems of
incorrect values reaching the rest of the system.
Rationality Check
Once the engine coolant temperature has st
abilised hot, the output of the intake air temperature sensor is compared at low and
high airflow
conditions. The test relies on the fact that the under bonnet temp
erature causes the intake air temperature to rise at idle co
mpared to high airflow
conditions, where the real external ambient
temperature is being read. These tests w
ill check that the sensor is correctly moun
ted and connected.
The tests are two-sided, but only one flow chart has been shown.
3. Primary Detection Parameter
Intake Air Temperature - meas
ured as thermistor voltage.
4. Fault Criteria Limits
Intake Air Temperature Circuit Low Input 0.059V - equivalent to 145o
C
Intake Air Temperature Circuit High Input 4.922V - equivalent to –40o
C
Intake Air Temperature rise/fall during rationality check approx 3o
C
5. Monitoring Conditions
The range check will take place whenever there is power to the ECM.
For the rationality check, the following co
nditions must be met in consecutive order:
i. engine coolant temperature is above a threshold (70o
C).
ii. engine operates at a constant mass airflow rate for a period of time.
iii. the average mass airflow ra
te changes at
a certain rate.
iv. engine maintains the new mass airflow 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.
Land Rover Revision Date: February 2004 Page 77 of 143
The rationality check will take place at least once per trip.
7. Criteria for Storing a Diagnostic Trouble Code
Two successive trips where the air
thermistor diagnostic indicates a failed intake air temperature sensor.
8. Criteria for Illuminating MIL
Two successive trips where the air
thermistor diagnostic indicates a failed intake air temperature sensor.
9. Criteria for Determining Out of Range Input Signals
Range check as above.
