Circuit Description
The intake air temperature (IAT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The IAT sensor's resistance is high if the air temperature is cold and low if the air temperature is warm. 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 receives a high voltage input if the air temperature is cold and a low voltage input if the air temperature is warm.
Condition for Running the DTC
| • | The engine coolant temperature at the engine start up is less than 30°C (86°F). |
| • | The engine has been running 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 trips during which the diagnostic runs, and a fault is not detected. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the Clear DTC Information function of the scan tool, 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 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 vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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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.
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This step checks for a faulty IAT sensor.
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This step checks the integrity of the 5 volt reference circuit of the IAT sensor .
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This step checks the integrity of the IAT sensor ground circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 |
Is the IAT value within the specified value of the ambient air temperature? | 0°C - 5°C (0°F - 9°F) | ||
|
Important: Observe the IAT sensor display on the scan tool continuously while performing the tests below.
Does the scan tool indicate a variable value or a fixed value? | -- | Go to Diagnostic Aids | ||
4 |
Does the scan tool indicate the specified value? | 119°C (246°F) | ||
Did the DMM indicate a resistance reading that was less than the specified value? | 0.5 ohms | |||
Using a DMM, measure the resistance of the IAT sensor ground circuit, from the sensor to the PCM. Did the DMM indicate a resistance reading that was less than the specified value? | 0.5 ohms | |||
7 | Repair the short to ground or the high resistance in the 5 volt reference circuit of the IAT sensor between the PCM and the sensor. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
8 | Repair the open circuit or the high resistance in the IAT sensor ground circuit between the PCM and the sensor. Refer to Wiring Repairs in Wiring Is the action complete? | -- | -- | |
9 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
10 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
11 |
Are any DTCs displayed on the scan tool? | -- | Go to the applicable DTC table | System OK |
