Circuit Description
The intake air temperature (IAT) sensor contains a semiconductor device which changes the resistance based on the temperature. The IAT sensor has a signal circuit and a low reference circuit. The powertrain control module (PCM) applies 5 volts on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine intake air temperature.
When the intake air is cold, the sensor or thermistor resistance is high. The PCM signal voltage is only pulled down a small amount through the sensor to a ground, therefore, the PCM senses a high signal voltage. When the intake air is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount, therefore, the PCM senses a low signal voltage.
When the PCM senses a signal voltage lower than the normal operating range of the sensor, this diagnostic trouble code (DTC) sets.
Conditions for Running the DTC
| • | DTCs P0102, P0103, P0117, P0118, P0502, or P0503 are not set. |
| • | The engine coolant temperature (ECT) is less than 135°C (275°F). |
| • | The engine run time is more than 30 seconds. |
| • | The vehicle speed is 40 km/h (25 mph) or more. |
Conditions for Setting the DTC
The IAT is more than 139°C (282°F) for 5 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 engine has not been started for more than 8 hours, the ECT and the IAT values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance . |
| • | If you determine that the DTC occurs intermittently, performing the DTC P1112 diagnostic table may isolate the cause of the fault. |
For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the malfunction is present.
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Using the Freeze Frame/Failure Records may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions that you observed, such as the RPM, the load, the vehicle speed, or the temperature . This procedure will isolate when the DTC failed.
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The IAT sensor is part of the MAF sensor. An IAT below -30°C (-22°F) indicates the PCM and the IAT wiring are OK.
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Disconnecting the PCM allows using the DMM in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.
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 above the specified value? | 139°C (282°F) | Go to Step 4 | Go to Step 3 | |
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |
Is the IAT at the specified value? | -39°C (-38°F) | Go to Step 6 | Go to Step 5 | |
Is the IAT signal circuit grounded? | -- | 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 | Use a scan tool in order to observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
