Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering 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. When the PCM detects an excessively low signal voltage on the intake air temperature sensor signal circuit. DTC P0112 will set.
Conditions for Running the DTC
| • | DTCs 501 and 502 are not set. |
| • | The engine has been running for over 10 seconds. |
| • | Vehicle speed is greater than 40 km/h (25 mph). |
Conditions for Setting the DTC
| • | IAT signal voltage indicates an intake air temperature greater than 135°C (275°F). |
| • | The above conditions are present for at least 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. |
Diagnostic Aids
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refers to the step numbers on the diagnostic table.
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Verifies that the fault is present.
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If DTC P0112 can be repeated only by duplicating the Freeze Frame/Failure Records conditions. Refer to the Temperature vs Resistance table. The table may be used to test the IAT sensor at various temperatures to 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 Diagnostic Aids.
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This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the parameter measure more than specified value? | 135°C (275°F) | Go to Step 4 | Go to Step 3 | |
Does the DTC reset? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Does the parameter measure less 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 | -- |
|
Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement . Replace the PCM. Did you complete the replacement? | -- | Go to Step 8 | -- | |
8 |
Does the scan tool indicate that this test ran and passed? | -- | Go to Step 9 | Go to Step 2 |
9 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | - | System OK | |
