P1112 - FAULT CODE - OBD2

P1112 ACURA, SATURN, BUICK, CADILLAC, SUZUKI, JEEP, CHEVROLET, CHRYSLER, DODGE, GMC, HONDA, ISUZU, KIA, MAZDA, PONTIAC: INTAKE AIR TEMPERATURE SENSOR CIRCUIT INTERMITTENT LOW VOLTAGE

The IAT (Intake Air Temperature) sensor has a semiconductor that can vary the resistance according to the temperature. This sensor is located in the air inlet of the induction system and has a signal circuit and a ground circuit. The Powertrain Control Module (PCM) sends to the IAT Sensor a voltage of approximately 5.0V in its signal circuit. Besides, the PCM monitors the changes of this voltage because of the variations of the resistance of the sensor in order to calculate the temperature of the intake air.

If the intake air temperature is low, the resistance of the sensor turns out to be high. Through this process, the signal voltage drops to a small amount across the sensor to the ground circuit. In this case, the PCM detects a high signal voltage or low temperature. On the other hand, the opposite occurs when the intake air is hot, as the resistance is low so the signal voltage is reduced to a greater degree, thus interpreting a low signal voltage or high temperature.

The P1112 OBDII fault code is a manufacturer-specific code that changes its meaning for each manufacturer.  This change is related to a voltage problem of the signal sent to the PCM by the IAT Sensor. If the PCM detects the temperature is too high, the signal voltage will drop below the allowable limit, and the P1112 code will be set.

• Check Engine light ON.
• Difficulty starting the engine during cold starts.
• Lack of engine power.
• Lower fuel efficiency.

Reasons to set the P1112 OBD2 diagnostic code:

• The inlet air temperature sensor wiring may be bad.
• The IAT sensor may be defective.
• The PCM may have programming errors.

Steps to troubleshoot the P1112 OBDII DTC are as follows:

• Consult the TBS (Technical Service Bulletins). These contain useful repair information.
• Inspect all the cables and connectors related to the IAT Sensor for damage due to burns, wear, or corrosion. Repair or replace any of these components that have such deficiencies.
• Perform electrical checks on the inlet air temperature sensor Compare the actual values with those specified by the manufacturer. If you find some differences, make the required repairs.
• Verify the good condition of the Intake Air Temperature Sensor. Follow the steps indicated by the manufacturer. If you determine that it is defective, replace it.