For 1990-2009 cars

### 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 intermittent low IAT signal voltage, indicating a high temperature, DTC P1112 sets.

### Conditions for Running the DTC

• | DTC P0500 is not set.

• | The engine run time is more than 45 seconds.

• | The vehicle speed is more than 40 km/h (25 mph).

### Conditions for Setting the DTC

• | The IAT sensor parameter is more than 128°C (262°F).

• | The condition exists intermittently for more than 6 seconds.

### Action Taken When the DTC Sets

• | The control module stores the DTC information into memory when the diagnostic runs and fails.

• | The malfunction indicator lamp (MIL) will not illuminate.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.

• | The driver information center, if equipped, may display a message.

### Conditions for Clearing the DTC

• | 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 non-emission related diagnostic.

• | Clear the DTC with a scan tool.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Observe the DTC Information with a scan tool. Is DTC P0112 set? | Go to DTC P0112 | Go to Step 3
3 | Test the IAT signal circuit between the IAT sensor and the PCM for an intermittent short to ground. Refer to Testing for Intermittent Conditions and Poor Connections or Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 4 | Go to Intermittent Conditions
4 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 5

5 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK