Circuit Description
The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air that enters the engine. The powertrain control module (PCM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high, and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. The PCM will set a diagnostic trouble code (DTC) if an excessively low IAT sensor signal voltage is detected.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0112, P0113, P0128, P0502, or P0503 are not set. |
| • | The engine has been running for over 10 seconds. |
| • | The vehicle speed is more than 42.3 km/h (25 mph). |
Conditions for Setting the DTC
The PCM detects that the IAT sensor temperature is more than 135°C (275°F) for more than 20 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step verifies that the fault is present.
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If DTC P0112 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance table. Use the table in order to test the IAT sensor at various temperatures. This procedure will evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the IAT sensor. If the IAT sensor appears to be OK, the fault is intermittent. Refer to Intermittent Conditions.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Is the IAT sensor more than the specified value? | 135°C (275°F) | Go to Step 4 | Go to Step 3 | |
Does the DTC set? | -- | Go to Step 4 | Go to Intermittent Conditions | |
4 |
Is the IAT sensor more than the specified value? | -37°C (-34°F) | Go to Step 6 | Go to Step 5 |
5 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 |
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Does the DTC run and pass? | -- | Go to Step 9 | Go to Step 2 |
9 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
