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 powertrain control module (PCM) 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 PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | DTCs P0116, P0117, P0118, P0125, P0128, P0722 are not set. |
| • | The engine run time is more than 10 seconds. |
| • | The vehicle speed sensor (VSS) indicates that vehicle speed is more than 40 km/h (25 mph). |
| • | The engine coolant temperature (ECT) is less than 121°C (250°F). |
| • | The diagnostic runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM detects that the IAT sensor parameter is more than 130°C (266°F) for more than 18 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
| • | When the vehicle is at ambient temperature, the IAT sensor and the engine coolant temperature (ECT) sensor should be relatively close to each other. Refer to Temperature Versus Resistance . |
| • | If an intermittent condition is suspected, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain 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 | Observe the intake air temperature (IAT) sensor parameter with a scan tool. Is the IAT sensor parameter more than the specified value? | 130°C (266°F) | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the IAT sensor parameter less than the specified value? | -36°C (-33°F) | Go to Step 6 | Go to Step 5 |
5 | Test the signal circuit of the IAT sensor for a short to ground or a short to the IAT low reference circuit and repair as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
6 | Test for an intermittent and for a poor connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 |
7 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
8 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 |
11 | 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 |
