Circuit Description
The Intake Air Temperature (IAT) sensor contains a device which changes the resistance based on the temperature (a thermistor). The IAT sensor is located in the mass air flow (MAF) sensor. The IAT sensor has a signal circuit and a ground circuit. The ECM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The ECM monitors any 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. Therefore, the ECM will sense a high signal voltage (low temperature). When the intake air is warm, the sensor resistance is low. This causes the ECM to sense a low signal voltage (high temperature).
When the ECM senses a signal voltage outside of the normal operating range of the sensor, this DTC will set.
Conditions for Running the DTC
The engine must be running for at least 3 minutes.
Conditions for Setting the DTC
| • | The IAT signal voltage indicates an intake air temperature that is more than 139°C (282°F). |
| OR |
| • | The IAT signal voltage indicates an intake air temperature that is at -40°C (-40°F). |
| • | The above condition is met for at least 10 seconds in idle. |
Action Taken When the DTC Sets
The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes. |
| • | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic. |
| • | The ECM battery voltage is interrupted. |
| • | The scan tool clears the MIL/DTC. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same Freeze Frame conditions, the RPM, the MAF, the vehicle speed, the temperature etc., that were noted. This process may help to recreate the malfunction.
-
The IAT sensor and the MAF sensor are replaced as an assembly. The IAT sensor is not to be serviced separately.
-
Perform the Idle Learn Procedure when replacing the ECM or throttle body.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
2 |
Is the IAT above the specified value? | 139°C (282°F) | Go to Step 6 | Go to Step 3 |
3 | Is the IAT at the specified value? | -40°C (-40°F) | Go to Step 8 | Go to Step 4 |
4 |
Is the IAT value affected by moving the harness or connectors? | -- | Go to Step 12 | Go to Step 5 |
Is this DTC set? | -- | Go to Step 6 | Go to Diagnostic Aids | |
6 |
Is the IAT at the specified value? | -40°C (-40°F) | Go to Step 17 | Go to Step 7 |
7 |
Is continuity indicated? | -- | Go to Step 13 | Go to Step 19 |
8 |
Is the IAT above the specified value? | 139°C (282°F) | Go to Step 16 | Go to Step 9 |
9 | Jumper the IAT signal circuit to a known good ground. Is the IAT above the specified value? | 139°C (282°F) | Go to Step 11 | Go to Step 10 |
10 |
Is continuity indicated? | -- | Go to Step 18 | Go to Step 14 |
11 |
Is continuity indicated? | -- | Go to Step 18 | Go to Step 15 |
12 | Repair the harness/connections as necessary. Is the action complete? | -- | Go to Step 20 | -- |
13 | Repair the signal circuit shorted to ground. Is the action complete? | -- | Go to Step 20 | -- |
14 | Repair the open/high resistance signal circuit. Is the action complete? | -- | Go to Step 20 | -- |
15 | Repair the open/high resistance ground circuit. Is the action complete? | -- | Go to Step 20 | -- |
16 | Check for a poor connection or poor terminal tension at the IAT/MAF sensor harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Did you find and correct a problem? | -- | Go to Step 20 | Go to Step 17 |
Replace the IAT/MAF sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 20 | -- | |
18 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Did you find and correct a problem? | -- | Go to Step 20 | Go to Step 19 |
|
Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 20 | -- | |
20 |
Does the scan tool indicate the diagnostic Passed? | -- | Go to Step 21 | Go to Step 2 |
21 | Does the scan tool display any additional, undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
