P0112

Diagnostic Chart:

Wiring Diagram:

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 the 5 volt reference circuit. When the air is cool, the resistance in the sensor measures high and the VCM senses a high voltage signal. It the air is warm, the sensor resistance measures low and the VCM senses a low voltage signal.

CONDITIONS FOR SETTING THE DTC

The following conditions will set the DTC:

^ No VSS DTCs

^ Vehicle speed is at least 2 MPH

^ Engine run time is greater than 100 seconds

ACTION TAKEN WHEN THE DTC SETS

The VCM turns ON the MIL when DTC P0112 is reported and 1 failure has occurred.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ 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 exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

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. It 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 Specifications / Electrical / Temperature vs Resistance.

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. It 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.