Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The PCM applies 5.0V 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 P0112 will set when the PCM detects an excessively low signal voltage on the intake air temperature sensor signal circuit.
Conditions for Running the DTC
| • | No active ECT sensor or VSS DTC present. |
| • | Engine running for over 10 seconds. |
| • | Vehicle speed is greater than 25 mph. |
Conditions for Setting the DTC
| • | IAT signal voltage indicates an intake air temperature greater than 135°C (275°F). |
| • | The above conditions are present for at least 30 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. |
| • | The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Check for the following conditions:
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Test Description
The number below refers to the step number on the Diagnostic Table:
-
Verifies that the fault is present.
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If DTC P0112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature Versus Resistance table. The table 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. If the IAT sensor appears to be OK, the fault is intermittent refer to Diagnostic Aids.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain on Board Diagnostic System Check Performed? | -- | ||
Is the intake air temperature greater than the specified value? | 130°C (266°F) | |||
Does scan tool indicate DTC P0112 failed this ignition? | -- | Go to Diagnostic Aids | ||
4 |
Is Intake Air Temperature below the specified value? | -30°C (-22°F) | ||
5 |
Is the IAT sensor signal circuit shorted to ground? | -- | ||
6 | Replace IAT Sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
7 | Repair IAT sensor signal circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
|
Important: : Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | ||
9 |
Does scan tool indicate DTC P0112 failed this ignition? | -- | System OK |
