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. If the PCM detects an intermittently low signal voltage on the intake air temperature sensor signal circuit DTC P1112 will set.
Conditions for Running the DTC
| • | DTCs P0502 or P503 are not set. |
| • | The engine has been running for over 10 seconds. |
| • | The vehicle speed is greater than 40.2 km/h (25 mph). |
| • | The above conditions are set for at least 5 seconds. |
Conditions for Setting the DTC
The IAT signal voltage intermittently indicates an intake air temperature greater than 135°C (275°F).
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Verifies that the malfunction is present.
-
If DTC P1112 can be repeated only by duplicating the Failure Records conditions, refer to 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.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Is DTC P0112 also set? | Go to DTC P0112 | Go to Step 3 | |
Was a condition found? | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Does the DTC run and pass? | Go to Step 5 | Go to Step 2 |
5 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
