Circuit Description
The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The engine control module (ECM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the resistance is high, and the ECM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the ECM to monitor a lower voltage. DTC P1111 will set when the ECM detects an intermittent high signal voltage in the intake air temperature sensor signal circuit or sensor.
Conditions for Setting the DTC
| • | The IAT is less than 149°C (300°F). |
| • | DTC P0502 is not set. |
| • | The engine has been running for over 2 minutes. |
| • | Vehicles speed is greater than or equal to 50 km/h (31 mph). |
Action Taken When the DTC Sets
| • | The ECM will substitute a default value for the IAT. |
| • | The ECM 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. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
Inspect for the following conditions:
| • | A poor connection at the ECM--Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal-to-wire connection. |
| • | A 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 Failure 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. |
| • | Use the Temperature vs. Resistance Values table to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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This step verifies the fault is present.
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If DTC P1112 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature Vs. Resistance Value Chart. The chart may be used to test the IAT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the IAT sensor.
Step | Action | Yes | No |
|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | Go to Step 2 | ||
Is DTC P0112 also set? | Go to applicable DTC table | Go to Step 3 | |
Inspect the intake air temperature (IAT) signal circuit between terminal 1 of the IAT sensor and terminal A23 of the engine control module (ECM) for an intermittent short to ground and repair as needed. Did you find and correct the condition? | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Does the scan tool indicate that this diagnostic has run and passed? | Go to Step 5 | Go to Step 2 |
5 | Are any DTCs displayed that have not been diagnosed? | Go to applicable DTC table | System OK |
