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. Therefore the PCM will sense a low signal voltage or a high temperature. If the PCM detects an excessively low IAT signal voltage, a high temperature indication, this DTC will set.
Conditions for Running the DTC
| • | DTCs P0117, P0118, P0125, P0502, P0503, P1114, or P1115 are not set. |
| • | The engine has been running for more than 10 seconds. |
| • | The vehicle speed is more than 40 km/h (25 mph). |
Conditions for Setting the DTC
| • | The IAT signal voltage indicates an intake air temperature of more than 134°C (274°F). |
| • | The above conditions are present for at least 20 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
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
| • | Inspect for a skewed or an incorrectly calibrated IAT sensor. Refer to Temperature Versus Resistance . |
| • | If DTC P0112 cannot be duplicated, the information included in the Failure Records can be useful in determining the vehicle mileage since the DTC was last set. |
| • | If the problem is intermittent, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The step 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 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 malfunction is intermittent. Refer to Diagnostic Aids.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Observe the IAT display on the scan tool. Is IAT more than the specified value? | 130°C (266°F) | Go to Step 4 | Go to Step 3 | |
Does the scan tool indicate DTC P0112 failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Is the IAT less than the specified value? | -38°C (-36°F) | Go to Step 6 | Go to Step 5 |
5 |
Is the IAT sensor signal circuit shorted to ground? | -- | Go to Step 7 | Go to Step 8 |
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 9 | -- |
7 | Repair the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 9 | -- |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 9 | -- |
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 |
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
