Circuit Description
The intake air temperature (IAT) sensor is a thermistor that measures the temperature of the air entering the engine. The powertrain control module (PCM) applies 5 volts to the IAT sensor through a pull-up resistor. When the intake air is cold, the sensor resistance is high and the PCM monitors 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. DTC P1112 is set when the PCM detects an intermittently low signal voltage on the IAT sensor signal circuit.
Conditions for Running the DTC
- No engine coolant temperature (ECT) sensor, mass air flow (MAF) sensor, or vehicle speed sensor (VSS) DTCs are present.
- The engine is running for over 10 seconds.
- The vehicle speed is more than 25 mph.
Conditions for Setting the DTC
IAT signal voltage intermittently indicates an intake air temperature greater than 134°C (274°F).
Action Taken When the DTC Sets
The PCM stores the conditions which were present when the DTC set as Fail Records data only.
Conditions for Clearing the MIL/DTC
| • | A history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC may be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Inspect for the following conditions:
| • | A faulty connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connections. |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on a scan tool while moving the connectors and wiring harnesses related to the IAT sensor. A change in the IAT display indicates the location of the malfunction. |
| • | A skewed or mis-scaled IAT sensor. Refer to Temperature vs Resistance . |
Reviewing the Fail 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 number(s) below refer to the step number(s) on the Diagnostic Table.
-
Verifies that the malfunction is present.
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If DTC P1112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature Vs. Resistance Values Table. The table may be used to test the intake air temperature (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 | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Use a scan tool in order to select DTC info, Last Test Fail and note any other DTCs set. Is DTC P0112 also set? | -- | Go to DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage | ||
Was a problem found? | -- | Go to Diagnostic Aids | ||
4 |
Does the scan tool indicate DTC P1112 failed? | -- | System OK |
