Circuit Description
The intake air temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor measures the temperature of the air entering the engine. The engine control module (ECM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit. If the ECM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The battery voltage is between 10-16 volts. |
Conditions for Setting the DTC
The ECM detects that the IAT signal voltage is less than 0.1 volt.
Action Taken When the DTC Sets
| • | The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records. |
| • | The ECM uses an IAT value of -29°C (-20.2°F) for engine starting. |
| • | The ECM uses an IAT value of 25°C (77°F) for engine running. |
| • | The ECM closes the exhaust gas recirculation (EGR) valve and holds to Close position. |
Condition for Clearing the DTC
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Important: The MAF sensor is heated and as a result the IAT sensor may indicate a higher than normal intake air temperature.
| • | When the vehicle is at ambient temperature, the IAT sensor and engine coolant temperature (ECT) sensor temperature should be relatively close to each other. |
| • | Use the Temperature vs. Resistance table to test the IAT sensor at various temperature levels to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature Versus Resistance . |
| • | For intermittent conditions, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||
2 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Diagnostic Aids | ||||
3 |
Is the IAT Sensor parameter less than the specified value? | -30°C (-22°F) | Go to Step 5 | Go to Step 4 | ||||
4 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6 | ||||
5 | Replace the IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | ||||
6 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 | ||||
7 |
Important: The new ECM must be programmed. Replace the ECM. Refer to, Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming . Did you complete the replacement? | -- | Go to Step 8 | -- | ||||
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
