For 1990-2009 cars
Engine Controls Components
Engine Data Sensors, A/C Refrig Press, TP, MAP, ECT, IAT
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The 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 Setting the DTC

• | No ECT sensor, MAF sensor or VSS DTC present.

• | The engine has been running for over 3 minutes.

• | Vehicle speed is less than 35 mph.

• | Mass Air Flow is less than 12 gm/s.

• | Engine Coolant Temperature is greater than 60°C (140°F).

• | IAT signal voltage intermittently indicates an intake air temperature less than -34°C (-29°F).

### Action Taken When the DTC Sets

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

• | The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

### Conditions for Clearing the MIL/DTC

• | A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool Clear Info function.

### Diagnostic Aids

Check for the following conditions:

• | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

#### DTC P1111 - IAT Sensor Circuit Intermittent High Voltage

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Select DTC info, Last Tst Fail and note any other DTCs set. Is DTC P0113 also set? | -- | Go to DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage | Go to Step 3
3 | Is DTC P1106, P1115, and/or P1121 also set? | -- | Go to Step 6 | Go to Step 4
4 |

1. Check for a poor sensor ground circuit terminal connection at the IAT sensor. Refer to Troubleshooting Procedures in Electrical Diagnosis.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to Step 10

Go to Step 5

5 |

1. Check for a poor IAT signal circuit terminal connection at the IAT sensor.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to Step 10

Go to Step 6

6 |

1. Check the IAT signal circuit between the IAT sensor connector and the PCM for an intermittent open.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to Step 10

Go to Step 7

7 |

1. Check the IAT signal circuit between the IAT sensor connector and the PCM for an intermittent short to voltage. Refer to Repair Procedures in Electrical Diagnosis.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 10

Go to Step 8

8 |

1. Check for a poor sensor ground circuit terminal connection at the PCM.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to Step 10

Go to Step 9

9 |

1. Check for an intermittent open or a faulty splice in the sensor ground circuit.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to Step 10

Refer to Diagnostic Aids

10 |

1. Review and record scan tool Fail Records data.
2. Clear DTCs.
3. Operate the vehicle within Fail Records conditions as noted.
4. Using a scan tool, monitor Specific DTC info for DTC P1111.

Does scan tool indicate DTC P1111 failed?

--

Go to Step 2

System OK