P0112

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor located in the fresh air duct to the throttle body in order to monitor the temperature of the air entering the throttle body. The VCM applies 5 volts to the sensor on 5 volt reference circuit. When the air is cool, the resistance in the sensor measures high and the VCM senses a high voltage signal. If the air is warm, the sensor resistance measures low and the VCM senses a low voltage signal. This DTC is a type A DTC.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

^ No VSS sensor DTCs.
^ Vehicle speed is at least 2 mph.
^ Engine run time is greater than 100 seconds.
^ Intake air temperature circuit voltage less than 0.82 volts.

ACTION TAKEN WHEN THE DTC SETS
The VCM sets the DTC P0112. The VCM turns on the Malfunction Indicator Lamp (MIL) when the P0112 is reported and 1 failure has occurred.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

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 IAT temperature or 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 waiver. 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.

TEST DESCRIPTION
The numbers below refer to the numbers on the diagnostic table.

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

2. If the IAT sensor circuit voltage measure less than 0.82 volts, the conditions for the DTC are still present and the problem is not intermittent.
3. This test bypasses the IAT sensor and confirms that the IAT signal circuit and the sensor ground circuit to the VCM are sound. Opening the signal circuit provides a high voltage input to the VCM. The VCM should recognize this high voltage and indicate a low IAT temperature.
4. This test determines if the IAT sensor signal circuit is shorted to the sensor ground.