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) P1112 will set when the PCM detects an intermittently low signal voltage on the intake air temperature sensor signal circuit.
Conditions for Running the DTC
| • | DTCs P0502 or P0503 are not set. |
| • | The engine has been running for over 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 more 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
| • | 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. |
| - | 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. |
| - | Skewed or mis-scaled IAT sensor--Refer to Temperature Versus Resistance . |
| • | Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition. |
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 | |
Did you find and correct the condition? | 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 | |
