The Intake Air Temperature Sensor (IATS) is installed into the Mass Air Flow Sensor (MAFS). The IATS uses a thermistor whose resistance changes with the temperature. The electrical resistance of the IATS decreases as the temperature increases, and increases as the temperature decreases. The 5 V power source in the PCM is supplied to the IATS via a resistor in the PCM. That is, the resistor in the PCM and the thermistor in the IATS are connected in series. When the resistance value of the thermistor in IATS changes according to the intake air temperature, the signal voltage also changes. Using this signal, the information of the intake air temperature, the PCM corrects basic fuel injection duration and ignition timing.
PCM monitors temperature changes resulting from soaking the vehicle. Therefore, Coolant temperature and Intake temperature should be changed. If PCM detects intake air temperature correlated to coolant temperature does not change PCM determines that a fault exists and a DTC is stored.
Item
Detection condition
Possible cause
DTC Strategy
Case 1
? Monitors the difference between the startup coolant and IAT values
? IATS
Case 2
? Monitors the difference between the startup IAT and coolant values
Enable Conditions
? Engine soaked time = 360min
? Engine running state
? No faults present
? IAT stored previous trip
? Startup Coolant Temperature > -20°C
? Airflow >15 g/s
? Vehicle speed >40kph
Threshold Value
? Startup Coolant - Startup IAT = 30°C
? Startup IAT - Startup Coolant = 20°C
Diagnosis Time
? Continuous (More than 1.25 second failure)
MIL On Condition
? No MIL ON (DTC only)
Temp. (°C/°F)
Resistance (k?)
-40(-40)
95.95 ~ 105.78
20(68)
3.42 ~ 3.61
-20(-4)
27.4 ~ 29.77
40(104)
1.43 ~ 1.5
0(32)
9.08 ~ 9.72
60(140)
0.66 ~ 0.69
10(50)
5.49 ~ 5.83
80(176)
0.33 ~ 0.34
Fig 1) Temperature : 94?
The output signals of IATS & ECTS change smoothly without any rapid changes. Those have almost same characteristic signal during the early period after start. It means that the temperatures of intake air and engine coolant are depended on the temperature of atmosphere. Meanwhile, during the warming up, the output signal of ECTS is going up increasingly. but, the output signal of IATS changes a little bit. even it may not change almost. It means that the heat of engine does not affect on the temperature of intake air.