Circuit Description
The intake air temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The 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. 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
| • | No active ECT sensor, MAF sensor or VSS DTCs are present. |
| • | The engine has been running for over 10 seconds. |
| • | Vehicle speed is greater than 25 mph. |
Conditions for Setting the DTC
IAT signal voltage intermittently indicates an intake air temperature greater than 135°C (275°F).
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.
Conditions for Clearing the MIL/DTC
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The history DTC clears after 40 malfunction free warm-up cycles. |
| • | The PCM receives a clear code command from the 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 table. |
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 numbers below refer the step numbers on the diagnostic table.
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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 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 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
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 |
Using a scan tool, monitor Specific DTC info for DTC P1112. Does the scan tool indicate DTC P1112 failed? | -- | System OK |
