The Intake Air Temperature (IAT) sensor measures the temperature of engine intake air. The Intake Air Temperature (IAT) sensor is a thermistor (a variable resistor that changes along with outside air temperature) in series with a fixed resistor in the ECM. The ECM applies 5V to the IAT sensor. The ECM monitors the voltage across the IAT sensor and converts it into a temperature reading. When the outside air temperature is cold the IAT sensor resistance is high, and when the outside air temperature is warm the IAT sensor resistance is low. Therefore, when the air temperature is cold the ECM will receive a high voltage input, and when the air temperature is warm the ECM will receive a low voltage input. The signal from IAT sensor is used for injection duration correction, ignition timing correction and idle speed correction(Air-density correction).
ECM monitors temperature changes resulting from soaking the vehicle. Therefore, Coolant temperature and Intake temperature should be changed. If ECM detects intake air temperature correlated to coolant temperature does not change ECM determines that a fault exists and a DTC is stored.
Item
Detecting Condition
Possible Cause
DTC Strategy
Rationality check
Poor connection or damaged harness
Faulty IAT sensor
Case 1
Enable
Conditions
Vehicle speed = 5KPH
Coolant temperature > 75?
Coolant temperature at start < 45?
Idle state
Threshold
Value
Max. temp – Min. temp < 1.5? (=2 times).
DiagnosticTime
10 sec
Case 2
Vehicle speed = 50KPH
Air mass : 20~300kg/h
No idle state and fuel cut off.
Max. temp – Min. temp < 1.5? (=2 times)
5 sec
Case 3
Time after start < 40s
Coolant temperature at start : -6.8~35.5?
Coolant temperature at engine stop = 80.3?
No block heater detected
Cold start detected
IAT - ECT > 39.8?
MIL ONCondition
NO MIL
Temperature [°C(°F)]
Resistance [kO]
-40 (-40)
40.93 ~ 48.35
20 (68)
2.31 ~ 2.57
-30 (-22)
23.43 ~ 27.34
25 (77)
1.90 ~ 2.10
-20 (-4)
13.89 ~ 16.03
30 (86)
1.56 ~ 1.74
-10 (14)
8.50 ~ 9.71
40 (104)
1.08 ~ 1.21
0 (32)
5.38 ~ 6.09
60 (140)
0.54 ~ 0.62
10 (50)
3.48 ~ 3.90
80 (176)
0.29 ~ 0.34