For 1990-2009 cars
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The intake air temperature (IAT) sensor is a thermistor (a variable resistor whose conductive value changes with temperature) 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 it into a temperature reading. When the outside air temperature is cold, the IAT sensor resistance is high, and when the outside air temperature is warm, the IAT sensor resistance is low. Therefore, when the air temperature is cold, the PCM will receive a high voltage input, and when the air temperature is warm, the PCM will receive a low voltage input.

### Conditions for Setting the DTC

• | The engine is running.

• | The IAT sensor signal indicates a smaller change in the voltage than expected during a 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 the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after three consecutively passing trips without a fault present.

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

• | Use the scan tool 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 in order to check the IAT sensor at various temperature levels and evaluate the possibility of a shifted (incorrectly calibrated) sensor. A shifted sensor could result in a DTC P0111. Refer to Temperature Versus Resistance .

If the DTC P0111 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0111 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0111 appears in the Not Ran Since Code Cleared list, the P0111 diagnostic has not yet run. When the DTC P0111 does not appear in the Not Ran Since Code Cleared list, the P0111 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0111 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

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

• | Backed out terminals

• | Improper mating of terminals

• | Broken electrical connector locks

• | Improperly formed or damaged terminals

• | Faulty terminal to wire connections

• | Physical damage to the wiring harness

• | A broken wire inside the insulation

• | Corrosion of electrical connections, splices, or terminals

If you cannot duplicate the DTC P0111, the information included in the Freeze Frame data can be useful in determining 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 some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then 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.

4. This step checks the integrity of the 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. Compare the IAT sensor value with the ambient air temperature.

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

--

Go to Step 3

Go to Step 4

3 | Important: When performing the test below, watch the IAT sensor reading on the scan tool. Look for a skip, a jump, or no movement in the IAT value while the temperature increases and decreases.

1. Remove the IAT sensor from the air cleaner housing.
2. Connect the IAT electrical connector to the IAT sensor.
3. Wrap a cool damp shop towel around the IAT sensor to lower the temperature while monitoring the IAT sensor value on the scan tool.
4. Remove the shop rag and place a warm damp shop towel around the IAT sensor while monitoring the IAT sensor value on the scan tool.

Did you observe a skip, jump, or no movement in value?

--

Go to Step 9

Go to Diagnostic Aids

4 |

1. Disconnect the IAT sensor electrical connector.
2. Jump the IAT electrical connector using a fused jumper.

Does the scan tool indicate the specified value?

165°C (329°F)

Go to Step 9

Go to Step 5

5 |

1. Disconnect the fused jumper.
2. Disconnect the PCM electrical connector.
3. Connect a DMM from the PCM connector terminal IAT 5 volt reference (harness side) to the IAT connector terminal 5 volt reference (harness side).
4. Measure the resistance of the wire.

Does the DMM read within the specified value?

0.50 ohms

Go to Step 6

Go to Step 7

6 |

1. Connect a DMM from the PCM connector terminal IAT ground circuit (harness side) to the IAT connector terminal ground circuit (harness side).
2. Measure the resistance of the wire.

Does the DMM read within the specified value?

0.50 ohms

Go to Step 10

Go to Step 8

7 | Repair a short to ground or 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 an open circuit or 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 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 11 | --
11 |

1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
2. Review the scan tool data.
3. Check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to Diagnostic Trouble Code (DTC) List

System OK