P1112

DTC P1112 INTAKE AIR TEMPERATURE INTERMITTENT LOW VOLTAGE




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)/engine control module (ECM) applies 5 volts through a pull-up resistor to the IAT sensor. When the intake air is cold, the resistance is high, and the PCM/ECM 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/ECM to monitor a lower voltage. DTC P1111 will set when the PCM/ECM detects an intermittently low signal voltage on the intake air temperature sensor signal circuit.

Conditions for Setting the DTC
- DTC P0502 not set
- Engine has been running for over 3 seconds.
- Vehicle speed is greater than 0 mph.

Action Taken When the DTC Sets
- The PCM/ECM will substitute a default value for intake air temperature.
- The Malfunction Indicator Lamp (MIL) will not illuminate.
- The PCM/ECM will store conditions which were present when the DTC was set as Failure Records data only. This information will not be stored as Freeze Frame data.
- DTC P1112 does not illuminate the MIL.

Conditions for Clearing the MIL/DTC
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool CLEAR INFO function or by disconnecting the PCM/ECM battery feed.

Diagnostic Aids
Check for the following conditions:
- Poor connection at the PCM/ECM. 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 fault.
- 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.
- Use the Temperature vs. Resistance Values table to evaluate the possibility of a skewed sensor.

Steps 1 To 5:

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
2. Verifies the fault is present.
3. If DTC P1112 can be repeated only by duplicating the Fail Records conditions, refer to the Temperature Vs. Resistance Value Chart. The chart 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.