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.
Checking output signals of IATS under detecting condition, if an ouput signal is intermittently below 0.1V, PCM sets P1112.
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Monitor the signal of IAT sensor | ● Poor Connection ● Short to ground in signal circuit. ● Faulty IATS ● Faulty PCM |
Enable Conditions | Case 1 | ● Engine running state ● No Vehicle speed sensor fault ● Vehicle speed > 50kph(30mph) |
Case 2 | ● Engine running time >120 sec. ● Time from IG "OFF" to IG "ON" > 360 min. | |
Threshold value | ● Intermittently Intake air temperature sensor’s voltage < 0.1V | |
Diagnosis Time | ● Continuous | |
MIL On Condition | ● DTC only(NO MIL ON) |
Temp. (°C/°F) | Resistance (kΩ) | Temp. (°C/°F) | Resistance (kΩ) |
-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.
