For 1990-2009 cars

### Circuit Description

The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5 volts through a pull up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower, causing the PCM to monitor a lower voltage. DTC P1111 will set when the PCM detects an intermittently high signal voltage on the intake air temperature sensor signal circuit.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0128, P0502, P0503, P1114, or P1115 are not set.

• | The vehicle speed is less than 56 km/h (35 mph).

• | The mass air flow is less than 12 g/s.

• | The engine coolant temperature is more than 60°C (140°F).

• | The engine run time is more than 3 minutes.

### Conditions for Setting the DTC

• | The IAT signal voltage indicates an intake air temperature that is intermittently less than -37°C (-35°F).

• | The conditions are present for up to 5 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
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | With a scan tool, select diagnostic trouble codes (DTC). Is DTC P0113 also set? | Go to DTC P0113 | Go to Step 3
3 | Is DTC P1106, P1115, and/or P1121 also set? | Go to Step 6 | Go to Step 4
4 | Inspect for a faulty low reference circuit 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 5
5 | Inspect for a faulty signal circuit connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 10 | Go to Step 6
6 | Test the signal circuit of the IAT sensor for an intermittent open. 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 | Test the signal circuit of the IAT sensor for an intermittent short to voltage. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 10 | Go to Step 8
8 | Inspect for a faulty sensor low reference circuit connection at the 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 | Test the low reference circuit of the IAT sensor for an intermittent open or a faulty splice. 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 Intermittent Conditions
10 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Failure Records conditions as noted.

Does the DTC reset?

Go to Step 2

System OK