For 1990-2009 cars
Engine Controls Components
Cell 20: Engine Data Sensors
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. A thermistor is a resistor whose value varies with temperature. If the air temperature is cold, the IAT sensor resistance is high. If the air temperature is warm, the sensor resistance is low. The IAT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the IAT sensor. The PCM monitors the voltage across the IAT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input if the air temperature is cold. The PCM will receive a low voltage input if the air temperature is warm.

### Condition for Running the DTC

• | The engine coolant temperature at the engine start is less than 30°C (86°F).

• | The engine has been running under the start conditions above for at least 10 minutes.

### Conditions for Setting the DTC

The IAT sensor signal indicates a smaller change than expected in the voltage input during the warm-up cycle.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time that the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the DTC

• | The MIL turns OFF after 3 consecutive passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the Clear DTC Information function, or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

Check for a faulty electrical connection to the PCM.

Use the Temperature vs Resistance table to check the IAT sensor at various temperature levels in order to evaluate the possibility of a shifted sensor. A shifted sensor could result in a DTC P0111. Refer to Temperature Versus Resistance .

An intermittent malfunction may be caused by a fault in the IAT sensor electrical circuit. Inspect the wiring harness and the components for any of the following conditions:

• | Backed out terminals

• | Incorrect mating of terminals

• | Broken electrical connector locks

• | Incorrectly formed terminals or damaged terminals

• | Faulty terminal-to-wire connections

• | Physical damage to the wiring harness

• | A broken wire inside the insulation

• | Corrosion of electrical connections, of splices, or of terminals

If DTC P0111 cannot be duplicated, the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to complete basic checks and to store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data that was taken when the fault occurred. The information is stored in the scan tool for later reference.

2. This step checks for a faulty IAT sensor.

3. This step checks the integrity of the 5 volt reference circuit of the IAT sensor .

4. This step checks the integrity of the IAT sensor ground circuit.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition, leaving the engine OFF.
2. Install a scan tool.
3. Let the engine cool to the ambient air temperature.
4. Compare the IAT sensor value with the ambient air temperature.

Is the IAT value within the specified value of the ambient air temperature?

0°C to 5°C (0°F to 9°F)

Go to Step 3

Go to Step 4

3 | Important: Observe the scan tool display for the IAT sensor continuously while performing the tests below.

1. Disconnect the IAT sensor electrical connector.
2. Remove the IAT sensor from the air cleaner assembly.
3. Connect the IAT sensor electrical connector to the IAT sensor.
4. Wrap a cool damp shop towel around the sensor in order to lower the temperature while monitoring the sensor parameter on the scan tool.
5. Remove the towel, and place a warm damp shop towel around the sensor while monitoring the sensor parameter on the scan tool.

Did the IAT display of the scan tool indicate a variable value or a fixed value?

--

Go to Step 9

Go to Diagnostic Aids

4 |

1. Disconnect the IAT sensor electrical connector.
2. Use a fused jumper in order to jumper the electrical connector for the IAT sensor on the harness side.

Does the scan tool indicate the specified value?

119°C (246°F)

Go to Step 9

Go to Step 5

5 |

1. Disconnect the fused jumper.
2. Disconnect the PCM electrical connector.
3. Use a DMM in order to measure the resistance of the IAT sensor input circuit between the sensor and the PCM.

Did the DMM indicate a resistance reading that was less than the specified value?

0.5 ohms

Go to Step 6

Go to Step 7

6 | Use the DMM in order to measure the resistance of the IAT sensor ground circuit between the sensor and the PCM . Did the DMM indicate a resistance reading that was less than the specified value? | 0.5 ohms | Go to Step 10 | Go to Step 8
7 | Repair the short to ground or the high resistance in the 5 volt reference circuit between the PCM and the IAT sensor. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 11 | --
8 | Repair the open or the high resistance in the ground circuit between the PCM and the IAT sensor. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 11 | --
9 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 11 | --
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 11 | --
11 |

1. Clear any DTCs, and road-test the vehicle within the Conditions for Setting the DTC.
2. Review the scan tool data, and inspect for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to the applicable DTC table

System OK