Circuit Description
The intake air temperature (IAT) sensor contains a semi-conductor device, which is called a thermistor. This device changes the resistance, which is based on temperature. The IAT sensor is part of the sensor assembly, which is called the mass airflow/intake air temperature (MAF/IAT). The IAT sensor has a signal circuit and a ground circuit. The powertrain control module (PCM) applies about 5 volts on the signal circuit to the sensor. The PCM monitors changes in this voltage which are caused by changes in the resistance of the sensor in order to determine the IAT.
When the intake air is cold, the sensor's resistance is high. The signal voltage of the PCM is only pulled down a small amount through the sensor to a ground. Therefore, the PCM senses a high signal voltage, or a low temperature. When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down more. Therefore, the PCM senses a low signal voltage, or a high temperature.
When the PCM senses a signal voltage that is lower than the normal operating range of the sensor, this DTC will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0128, P0502, or P0503 are not set. |
| • | The engine run time is more than 30 seconds. |
| • | The engine coolant temperature (ECT) is less than 135°C (275°F). |
Conditions for Setting the DTC
| • | The intake air temperature (IAT) is more than 139°C (282°F). |
| • | The vehicle speed is more than 40 km/h (25 mph). |
| • | All conditions exist for 4.5 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
Important:
• Before you service the PCM or the throttle actuator control (TAC)
module, remove any debris from the module connector surfaces. Inspect the
module connector gaskets if you diagnose the modules, or
replace the modules. Verify that the gaskets are correctly installed.
The gaskets prevent debris from contaminating the PCM module or the TAC
module. • Use the J 35616
Connector Test Adapter Kit for any test that requires probing
the PCM or probing a component harness connector. Using this kit prevents
damage to the harness and component terminals. Refer to
Using Connector Test Adapters
in
Wiring Systems.
| • | If the engine has sat overnight, 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 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.
-
This step determines if the malfunction is present.
-
Use the Freeze Frame/Failure Records in order to locate an intermittent condition. This information may help determine how many miles occurred since the DTC set. The Fail Counter and the Pass Counter may help determine the number of ignition cycles that the diagnostic test reported a pass or a fail. In order to isolate under what conditions the DTC failed, operate the vehicle within the same Freeze Frame conditions that you observed. Check the data regarding the following conditions:
-
An IAT that is less than -30°C (-22°F) indicates that the PCM and the IAT wiring are OK.
-
Disconnecting the PCM allows you to use the DMM in order to test the continuity of the circuits. This procedures helps to locate an open or a shorted circuit.
| • | The RPM |
| • | The vehicle load |
| • | The vehicle speed |
| • | The temperature |
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 more than 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 | |||||||||
Did you find and repair the condition? | -- | Go to Step 8 | Go to Step 7 | |||||||||
6 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/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 in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
