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. 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 DTCs |
| • | Vehicle speed is greater than 2 mph |
| • | Engine run time is greater than 100 seconds |
| • | IAT circuit voltage less than 0.82 V |
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 or 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. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
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. 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 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 .
Test Description
The numbers below refer to the numbers on the diagnostic table.
Important: Use the same diagnostic test equipment for all the measurements.
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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.
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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 determines if the IAT sensor signal circuit is shorted to the sensor ground.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear DTC Information 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. Are any additional DTCs stored? | -- | Go to The Applicable DTC Tables | Go to Diagnostic Aids |
6 | Repair the short to the ground in the IAT 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: When replacing the VCM, the new VCM will need to be programmed. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
9 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
10 | Use the scan tool in order to display the Capture Info and the Review Capture Info function. Are there any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
