P0112

Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor. The control module (PCM/VCM) supplies the IAT sensor a reference voltage on the IAT sensor signal circuit and a ground circuit. When the IAT sensor resistance is high (cold sensor), the IAT sensor signal voltage remains near the supplied voltage, and decreases the signal voltage as the sensor warms. The control module monitors the IAT sensor signal circuit in order to calculate the temperature of the air entering the engine.

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 (3 km/h)
^ 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 Control Module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC
^ The Control Module 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 start-up 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
The IAT sensor indicates the temperature of the ambient air entering the throttle body. The IAT sensor temperature should read very close to the temperature of the outside air. The IAT sensor 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. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the numbers on the diagnostic table.

Important: Use the same diagnostic test equipment for all the measurements.

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. Disconnecting the IAT sensor harness could also set additional IAT related codes.