Circuit Description
The Intake Air Temperature (IAT) sensor is located in the fresh air duct to the throttle body. The Intake Air Temperature (IAT) sensor is a thermistor. The VCM uses the IAT 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 will read high, and the VCM will sense a high voltage signal. If the air is warm, the sensor resistance will read low, and the VCM will sense a low voltage signal. The DTC P1111 is a type D DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | No ECT DTCs |
| • | No VS DTCs |
| • | No MAF DTCs |
| • | The vehicle speed is less than 2 mph. |
| • | The engine coolant temperature greater than 84°C. |
| • | Engine run time is greater than 100 seconds |
Action Taken When the DTC Sets
The VCM stores the DTC in History if the VCM detects an intermittent problem.
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. The air temperature should rise gradually as the engine warms up and the underhood temperature increases. If the DTC P1111 is set, the problem is intermittent. Check for poor connections at the VCM and IAT sensor by wiggling the connector gently and monitoring the IAT temperature or IAT voltage on the scan tool. If the voltage waivers, repair the connector 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 temperature is less than -37° C, then the conditions for the DTC are still present and the problem is not an intermittent.
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This test will bypass the IAT sensor and will confirm that the IAT signal circuit and the sensor ground circuit to the VCM are sound. Grounding the signal circuit will provide a low voltage input to the VCM. The VCM should recognize this low voltage and indicate a high IAT temperature.
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This test will determine if the IAT sensor signal circuit is OK. If the scan tool indicates a high IAT temperature, the sensor ground is open. If the scan tool does not indicate a high temperature, the IAT signal circuit is open.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs use the scan tool to record the freeze frame and failure records for reference because the 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 greater than the specified value? | 4.9V | |||
Does the scan tool display a IAT sensor voltage less the specified value? | 0.82V | |||
Jumper the IAT sensor signal circuit to a known good ground. Does the scan tool display a IAT sensor voltage less the specified value? | 0.82V | |||
5 | Is DTC P0123 also set? | -- | Go to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage | |
6 | DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored refer to those Tables first. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | |
7 | Inspect the sensor connector and VCM connector for proper connection. Was a problem found? | -- | ||
8 | Check the IAT sensor ground circuit for an open between the IAT sensor and the VCM. Was a problem found? | -- | ||
9 | Check the IAT sensor signal circuit for an open between the IAT sensor and the VCM. Was a problem found? | -- | ||
10 | Repair the circuit as necessary. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
11 | Replace the IAT sensor. Refer to IAT Sensor Replacement . Is the action complete? | -- | -- | |
12 | Replace the VCM. Important: If the VCM is faulty, the new VCM must be programmed. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
14 | 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 |
