Circuit Description
The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM monitors 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 is set when the PCM detects an excessively low signal voltage on the intake air temperature sensor signal circuit.
Conditions for Running the DTC
| • | No engine coolant temperature (ECT) sensor, mass air flow (MAF) sensor, or vehicle speed sensor (VSS) DTCs are present. |
| • | The engine has run for over 10 seconds. |
| • | Vehicle speed is more than 25 mph. |
Conditions for Setting the DTC
| • | The IAT signal voltage indicates an intake air temperature more than 134°C (274°F). |
| • | The above conditions are present for at least 20 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has run and failed. |
| • | The PCM stores conditions which were present when the DTC set as Freeze Frame and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL off during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC may be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Inspect for the following conditions:
| • | A faulty connection at the PCM. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections. |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving the connectors and the wiring harnesses related to the IAT sensor. A change in the IAT display indicates the location of the malfunction. |
| • | A skewed or mis-scaled IAT sensor. Refer to Temperature vs Resistance . |
If DTC P0112 cannot be duplicated, the information included in the Fail Records data may be useful in determining vehicle mileage since the DTC was last set.
Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table:
-
Verifies that the malfunction is present
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If DTC P0112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature vs Resistance . The table may be used to test the intake air temperature (IAT) sensor at various temperatures in order 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 malfunction 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 replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the intake air temperature (IAT) more than specified value? | 130°C (266°F) | |||
Does the scan tool indicate DTC P0112 Failed This Ign? | -- | Go to Diagnostic Aids | ||
4 |
Is the IAT less than the specified value? | -38°C (-36°F) | ||
5 |
Is the IAT sensor signal circuit shorted to ground? | -- | ||
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the repair? | -- | -- | |
7 | Repair the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the repair? | -- | -- | ||
9 |
Does the scan tool indicate DTC P0112 Failed This Ign? | -- | System OK |
