Circuit Description
The intake air temperature (IAT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5-volt reference and a ground to the sensor. When the air is cold, the resistance is high and the IAT signal voltage will be high. If the intake air is warm the resistance is low, and the IAT signal voltage will be low.
Conditions for Running the DTC
| • | The engine run time is more than 320 seconds. |
| • | The engine coolant temperature (ECT) is more than -40°C (-6°F). |
| • | The vehicle speed sensor indicates that the vehicle speed is less than 15 mph (24 km/h). |
Conditions for Setting the DTC
The IAT sensor signal voltage indicates that the intake air temperature is less than -40°C (-6°F) for 3.125 seconds.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with fault active. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The coolant fan turns ON. |
| • | The PCM will default to 60°C (140°F) for intake air temperature. The scan tool will not the show the defaulted value. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
| • | If the vehicle is at ambient temperature, compare the IAT sensor to the ECT sensor. The IAT sensor and the ECT sensor should be relatively close to each other. |
| • | Use the Temperature vs. Resistance Values table, refer to Temperature vs Resistance to evaluate the possibility of a skewed sensor. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Important: Use the same diagnostic test equipment for all the measurements.
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If the intake air temperature (IAT) sensor circuit voltage measures more than 4.9 volts, the conditions for the DTC are still present, and the problem is not 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 PCM are sound. Grounding the IAT sensor signal circuit will provide a low voltage input to the PCM. The PCM should recognize this low voltage and indicate a high IAT temperature.
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This test determines if the IAT sensor signal circuit is okay. If the scan tool does not indicate a high IAT temperature, the IAT signal circuit is open.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the IAT sensor temperature less than the specified value? | -30°C (-22°F) | |||
Does the scan tool display an IAT sensor temperature more than the specified value? | 130°C (266°F) | |||
Jumper the IAT sensor signal circuit to a ground. Does the scan tool display an IAT sensor temperature more than the specified value? | 130°C (266°F) | |||
5 |
Is the voltage on the DMM more than the specified value? | 0.0 V | ||
6 | The DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Aids | |
7 | Check the IAT sensor harness connector and the PCM connector for a faulty connection. Refer to Connector Repairs . Did you find a problem? | -- | ||
8 | Check the IAT sensor ground circuit for an open or faulty connection between the IAT sensor and the PCM. Refer to Connector Repairs . Did you find a problem? | -- | ||
9 | Check the IAT sensor signal circuit for an open or faulty connection between the IAT sensor and the PCM. Refer to Connector Repairs . Did you find a problem? | -- | ||
10 | Repair the short to voltage in the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 | Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |
12 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
13 |
Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | |
14 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
15 | Does the scan tool display any additional undiagnosed DTCs? | -- | System OK |
