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 excessively high IAT signal voltage, indicating a low temperature, DTC P1111 sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1111 Intake Air temperature (IAT) Sensor Circuit Intermittent High Voltage

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0117, P0118, P0502, P0503 are not set.

• | The engine run time is more than 10 seconds.

• | The vehicle speed sensor (VSS) indicates that vehicle speed is less than 1.6 km/h (1 mph).

• | The engine coolant temperature (ECT) is more than 50°C (122°F).

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

### Conditions for Setting the DTC

The PCM detects that the IAT sensor parameter is less than -39°C (-38°F) intermittently for more than 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.

### Test Description

The number below refers to the step number on the diagnostic table.

1. This step tests for the proper operation of the circuit in the low voltage range.

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
2 | Observe the intake air temperature (IAT) sensor parameter with a scan tool. Is the IAT sensor parameter less than the specified value? | -39°C (-38°F) | Go to Step 4 | Go to Step 3
3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 90 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections

4 |

1. Disconnect the mass air flow (MAF)/IAT sensor.
2. Connect a DMM between the signal circuit of the IAT sensor and a good ground.

Is the voltage greater than the specified value?

5.2 V

Go to Step 5

Go to Step 6

5 | Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test the signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12
6 |

1. Connect a 3-amp fused jumper wire between the signal circuit of the IAT sensor and the low reference circuit of the IAT sensor.
2. Observe the IAT sensor parameter with a scan tool.

Is the IAT sensor parameter greater than the specified value?

149°C (300°F)

Go to Step 10

Go to Step 7

7 |

1. Connect a 3-amp fused jumper wire between the signal circuit of the IAT sensor and a good ground.
2. Observe the IAT sensor parameter with a scan tool.

Is the IAT sensor parameter greater than the specified value?

149°C (300°F)

Go to Step 9

Go to Step 8

8 | Test the signal circuit of the IAT sensor for an intermittent open circuit or high resistance. Refer to Circuit Testing and to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12
9 | Test the IAT sensor low reference circuit for an intermittent high resistance or an open. Refer to Circuit Testing and to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12
10 | Test the IAT signal circuit for an intermittent short to any 5-volt reference circuit. Refer to Circuit Testing and to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11
11 | Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test for an intermittent and for a poor connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13
12 | 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 to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
13 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
14 | Replace the PCM. Refer to Control Module References . Did you complete the replacement? | -- | Go to Step 15 | --
15 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 90 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 16

16 | Observe the Capture Info with a scan tool. Have any other DTCs not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK