P0112

DTC P0112 IAT Sensor Circuit Low Voltage




Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor located in the air inlet duct to the throttle Body. The IAT sensor has a signal circuit and a ground circuit. The signal circuit has 5 volts applied to it by the VCM. When the air is cool, the resistance of the IAT sensor is high and the VCM senses a high signal voltage. When the inlet air warms, the sensor resistance decreases and the VCM will detect a lower signal voltage at the signal circuit input.

This DTC is designed to detect an IAT sensor signal voltage lower than possible in a normally operating IAT sensor.

Conditions for Running the DTC
- No active VS sensor DTCs
- The vehicle speed is above 2 MPH
- The engine has been running for more than 100 seconds

Conditions for Setting the DTC
The IAT voltage is below a calibrated value for more than 5 seconds.

Action Taken When the DTC Sets
- The VCM illuminates the MIL (Malfunction Indicator Lamp) if a failure is detected during 2 consecutive key cycles.
- The VCM will set the DTC and records the operating conditions at the time the diagnostic fails. The VCM stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
- The VCM turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22 °C (40 °F) from the startup coolant temperature and the engine coolant temperature is more than 70 °C (158 °F) during the same ignition cycle).
- Use the scan tool Clear Information function.

Diagnostic Aids
A scan tool indicates the temperature of the ambient air entering the throttle Body. The air temperature should read very close to the temperature of the outside air. The air temperature should rise gradually as the engine warms up and the underhood temperature increases. If DTC P1112 is set, the problem is intermittent. Check for a short to ground in the IAT sensor signal circuit. This may be accomplished by moving the VCM harness at various locations and monitoring the IAT temperature or the IAT voltage on the scan tool. If the voltage varies, look for a short to ground in the area of the harness that caused the variance. Also, a sensor may become skewed or mis-scaled. The Temperature vs. Resistance Value Table will help to detect a skewed sensor. Refer to Temperature vs Resistance.

An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis.

If a repair is necessary, then refer to Wiring Repairs or Connector Repairs.

Step 1:

Steps 2 - 7:

Steps 8 - 10:

Test Description
The numbers below refer to the numbers on the diagnostic table.
2. If the IAT sensor circuit voltage measures less than 0.82 volts, the conditions for the DTC are still present and the problem is not intermittent.
3. Disconnecting the IAT sensor harness connector will provide a high voltage input to the VCM. The VCM should recognize this high voltage and indicate a low IAT temperature on the scan tool.