Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor located in the fresh air duct to the throttle body. The IAT monitors 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 will measure high, and the VCM senses a high voltage signal. If the air is warm, the sensor resistance will measure low, and the VCM senses a low voltage signal. This DTC is a type D DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | No VS sensor DTCs |
| • | The vehicle speed is at least 2 mph. |
| • | The engine run time is greater than 100 seconds. |
| • | The intake air temperature circuit voltage is less than 0.82 volts. |
Action Taken When the DTC Sets
The VCM sets the DTC and turns the MIL ON when this DTC is reported and 1 failure has occurred.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL 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 (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (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 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. Accomplish this 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 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 step numbers on the diagnostic table.
Important: Be sure to use the same diagnostic test equipment for all measurements.
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If IAT sensor circuit voltage is less than 0.82 volts, then the conditions for the DTC are still present and the problem is not intermittent.
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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.
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This test will determine if the IAT sensor signal circuit is shorted to sensor ground.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Is the IAT sensor voltage less than the specified value? | 0.82 V | |||
Is the IAT sensor voltage greater than the specified value? | 4.0 V | |||
Is the resistance at the specified value? | ∞ | |||
5 | The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | |
6 | Repair the short to ground in the IAT sensor signal circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
7 | Replace the IAT sensor. Refer to IAT Sensor Replacement . Is the action complete? | -- | -- | |
8 | Replace the VCM. Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
9 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
10 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
