Circuit Description
The intake air temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. 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, and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. 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. |
| OR |
| • | The engine is running for more than 2 minutes. |
| • | DTC P0112 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The IAT Sensor parameter is more than 128°C (262°F), for more than one second.
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. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Are DTCs P0641 or P0651 set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 3 |
3 |
Important: The cooling fans are commanded ON when certain DTCs are set. Observe the IAT Sensor parameter with a scan tool. Is the IAT Sensor parameter more than the specified value? | 128°C (262°F) | Go to Step 5 | Go to Step 4 |
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Inducing Intermittent Fault Conditions in Wiring Systems and Intermittent Conditions |
5 |
Is the IAT Sensor parameter less than the specified value? | -39°C (-38°F) | Go to Step 7 | Go to Step 6 |
6 | Test the signal circuit of the IAT sensor for a short to ground or for a short to the IAT low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 |
7 | Test for an intermittent and for a poor connection at the MAF/IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 |
8 | Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 |
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
