P1112

DTC P1112 Intake Air Temperature (IAT) Sensor Circuit - Intermittent Low Input:

Intake Air Temperature (IAT) Sensor Circuit:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor located in the fresh air duct to the throttle body and is used to monitor the temperature of the air entering the throttle body. The Vehicle Control Module-A (VCM-A) applies 5 volts to the sensor on CKT 472. When the air is cool, the resistance in the sensor will be high and the VCM-A will sense a high voltage signal. If the air is warm, the sensor resistance will be low and the VCM-A will sense a low voltage signal. DTC P1112 is a type "D" DTC.

DTC P1112 WILL SET WHEN
^ No Vehicle Speed Sensor (VSS) DTCs.
^ Vehicle speed is greater than 1 mph.
^ Engine run time is greater than 4 minutes.
^ Intake air temperature circuit voltage less than 0.82V.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
The VCM-A will store DTC P1112 to history if an intermittent problem is detected.

DTC P1112 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

Important
^ Be sure to use the same diagnostic test equipment for all measurements.

1. If IAT sensor circuit voltage is less than 0.82V, then the conditions for the DTC are still present and the problem is not intermittent.
2. This test will bypass the IAT sensor and will confirm that the IAT signal circuit and the sensor ground circuit to the VCM-A are sound. Opening the signal circuit will provide a high voltage input to the VCM-A. The VCM-A should recognize this high voltage and indicate a low IAT temperature.
3. This test will determine if the IAT sensor signal circuit is shorted to sensor ground.

DIAGNOSTIC AIDS
A scan tool indicates the temperature of the ambient air entering the throttle body. The air temperature should be very close to the temperature of the outside air and 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-A 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" scale at the bottom of the diagnostic chart will help to detect a "skewed" sensor.