Circuit Description
The Intake Air Temperature (IAT) sensor contains a semiconductor device which changes resistance based on temperature (a thermistor). The IAT sensor mounts in the air intake passage of the engine air induction system. The IAT sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor in order to determine the intake air temperature.
When the intake air is cold, the sensor (thermistor) resistance is high, and the PCMs signal voltage is only pulled down a small amount through the sensor to ground. The PCM senses a high signal voltage (low temperature). When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense a low signal voltage (high temperature).
When the PCM senses a signal voltage lower than the normal operating range of the sensor.
Conditions for Running the DTC
| • | DTC(s) P0102, P0103, P0117, P0118, are not set. |
| • | Engine operates longer than 2 minutes. |
| • | Vehicle speed is greater than or equal to 2 mph. |
Conditions for Setting the DTC
| • | Intake Air Temperature is greater than 139°C (282°F). |
| • | All above conditions exist for 0.3 second. |
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated.
Conditions for Clearing the MIL/DTC
| Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than 3 drive trips. Review Freeze Frame and Failure Records for the last failure conditions. |
| • | The PCM 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. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | Disconnect the PCM 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. 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 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 Temperature vs Resistance .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the malfunction is present.
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Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
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An intake air temperature below -30°C (-22°F) indicates the PCM and the IAT wiring are OK.
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Disconnecting the PCM allows using the DMM J 39200 in order to check continuity of the circuits. This aids in locating an open or a shorted circuit.
Step
| Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the IAT above the specified value? | 139°C (282°F) | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Is the IAT at the specified value? | -39°C (-38°F) | |||
Is the IAT signal circuit grounded? | -- | |||
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
7 |
Important:: Reprogram the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
8 |
Does the scan tool indicate that this test ran and passed? | -- | ||
9 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
