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 the diagnostic trouble code (DTC) P1112 will set.
Conditions for Running the DTC
| • | DTCs P0501 or P0502 are not set. |
| • | The engine has been running for more 10 seconds. |
| • | The vehicle speed is more than 40 km/h (25 mph). |
| • | The above conditions are present for at least 5 seconds |
Conditions for Setting the DTC
IAT signal voltage intermittently indicates an intake air temperature that is 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
Inspect for the following conditions.
Many situations may lead to an intermittent condition. The following list is to be used as a guide to assist in detecting an intermittent.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection. |
| Use a corresponding mating terminal to test for proper tension. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for diagnosis and repair. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for diagnosis and repair. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
2 | Is DTC P0112 set? | Go to DTC P0112 | Go to Step 3 |
3 |
Did you find and correct the condition? | Go to Step 4 | Go to Diagnostic Aids |
4 |
Does the scan tool indicate that this test ran and passed? | Go to Step 5 | System OK |
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 | |
