Circuit Description
The intake air temperature (IAT) sensor contains a semiconductor device which changes resistance based on temperature. The IAT sensor is located in the air intake passage of the engine air induction system. The IAT sensor has a signal circuit and a ground circuit. The powertrain control module (PCM) applies about 5 volts on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine intake air temperature.
When the intake air is cold, the sensor resistance is high, and the PCM signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM will sense a high signal voltage or a low temperature. When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense a low signal voltage or a high temperature.
Conditions for Running the DTC
| • | No ECT sensor or VSS DTCs present. |
| • | The engine has been 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 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) 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 turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (current DTC) clears when the diagnostic runs and does not fail. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | Use a scan tool in order to clear the MIL/DTC. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description , Clearing Diagnostic Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Check for a skewed or mis-scaled IAT Sensor. Refer to the Temperature vs Resistance table .
If DTC P0112 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.
If the problem is intermittent, refer to Intermittent Conditions .
Test Description
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 Failure Records conditions, refer to the Temperature vs Resistance . 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 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 being 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? | -- | ||
Observe the IAT display on the scan tool. Is IAT greater than the specified value? | 130°C (266°F) | |||
Does the scan tool indicate DTC P0112 failed this ign? | -- | Refer to Diagnostic Aids | ||
4 |
Is 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 . . Is the action complete? | -- | -- | |
7 | Repair the IAT sensor signal circuit. Is the action complete? | -- | -- | |
Replace the PCM. Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
9 |
Does the scan tool indicate that this test ran and passed? | -- | ||
10 | Review Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table
| System OK |
