Circuit Description
The intake air temperature (IAT) sensor uses a thermistor to control the signal voltage to the PCM. The PCM supplies a 5-volt reference and a ground to the sensor. When the air is cold the resistance will be high, therefore PCM terminal J1-30 voltage will be high. If the intake air is warm, resistance will be low, therefore PCM terminal J1-30 voltage will be low.
Conditions for Setting
| • | The engine run time is greater than 320 seconds. |
| • | The vehicle speed sensor indicates that vehicle speed is greater than 24 km/h (15 mph). |
| • | The IAT sensor signal voltage indicates that the intake air temperature is greater than 128°C (262°F). |
Action Taken
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will default to 60°C (140°F) for intake air temperature. The scan tool will not the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
| • | If the vehicle is at ambient temperature, compare the IAT sensor to the ECT sensor. The IAT sensor and the ECT sensor should be within 3 degrees of each other. |
| • | DTCs P0112 and P0121, shorted at the same time could be the result of an open CKT 452. |
| • | Use the Temperature vs. Resistance table below to evaluate the possibility of a skewed sensor. |
°C | °F | OHMS |
|---|---|---|
Temperature vs Resistance Values (approximate) | ||
212 | 100 | 177 |
194 | 90 | 241 |
176 | 80 | 332 |
158 | 70 | 467 |
140 | 60 | 667 |
122 | 50 | 973 |
113 | 45 | 1188 |
104 | 40 | 1459 |
95 | 35 | 1802 |
86 | 30 | 2238 |
77 | 25 | 2796 |
68 | 20 | 3520 |
59 | 15 | 4450 |
50 | 10 | 5670 |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check perform? | -- | Go to Step 2 | |
2 |
Is the IAT sensor value greater than the specified value? | 128°C (262°F) | Go to Step 4 | Go to Step 3 |
3 |
Is the IAT sensor value greater than the specified value? | 128°C (262°F) | Go to Step 5 | Go to Diagnostic Aids |
4 |
Is the IAT sensor value greater than the specified value? | -30°C (-22°F) | Go to Step 5 | Go to Step 6 |
5 |
Is a repair necessary? | -- | Go to Step 7 | |
6 | Replace the IAT sensor. Is the action complete? | -- | -- | |
7 | Replace the PCM. Is the action complete? | -- | -- | |
