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 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. Diagnostic trouble code (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
| • | DTCs P0502 and P0503 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 that is more than 135°C (275°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
Check for the following conditions:
| • | Poor connection at the PCM--Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and 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 malfunction. |
| • | A skewed or mis-scaled IAT sensor--Refer to Temperature Versus Resistance . |
If DTC P0112 cannot be duplicated, the information included in the Failure Records data can be useful in determining the vehicle mileage since the DTC was last set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step verifies that the malfunction is present.
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If DTC P0112 can be repeated only by duplicating the Failure Records conditions. The table may be used in order to test the 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 being replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Is the Intake Air Temp more than specified value? | 135°C (275°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 intake air temperature less than the specified value? | -38°C (-36°F) | Go to Step 6 | Go to Step 5 |
5 |
Was a problem found? | -- | Go to Step 8 | Go to Step 7 |
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 8 | -- |
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | |
8 |
Does the DTC run and pass? | -- | Go to Step 9 | Go to Step 2 |
9 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
