Circuit Description
The intake-air temperature (IAT) sensor contains a semi-conductor device, which is called a thermistor. This device changes the resistance which is based on temperature. The IAT sensor is part of the sensor assembly which is called the mass airflow/intake air temperature (MAF/IAT). The IAT sensor has a signal circuit and a ground circuit. The powertrain control module (PCM) applies about 5 volts on the signal circuit to the sensor. The PCM monitors changes in this voltage which is caused by changes in the resistance of the sensor in order to determine the IAT.
When the intake air is cold the sensor, or thermistor resistance is high. The signal voltage of the PCM is only pulled down a small amount through the sensor to a ground. Therefore, the PCM senses a high signal voltage, or a low temperature. When the intake air is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount and the PCM senses a low signal voltage, or a high temperature.
When the PCM senses a signal voltage that is higher than the normal operating range of the sensor, this diagnostic trouble code (DTC) will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0128, P0502, or P0503 are not set. |
| • | The engine coolant temperature (ECT) is more than 0°C (32°F). |
| • | The vehicle speed is less than 11 km/h (7 mph). |
| • | The mass air flow is less than 15 g/s. |
| • | The engine run time is more than 100 seconds. |
Conditions for Setting the DTC
| • | The intake air temperature (IAT) is less than -35°C (-31°F). |
| • | All conditions exist for 4.5 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Important:
• Before you service the PCM or the throttle actuator control (TAC)
module, remove any debris from the module connector surfaces. Inspect the
module connector gaskets if you diagnose the modules, or
replace the modules. Verify that the gaskets are correctly installed.
The gaskets prevent debris from contaminating the PCM module or the
TAC module. • Use the J 35616
Connector Test Adapter Kit for any test that requires
probing the PCM or probing a component harness connector. Using this
kit prevents damage to the harness and component terminals.
Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | If the engine has sat overnight, the ECT and the IAT values should display within a few degrees of each other. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance . |
| • | If you determine that the DTC occurs intermittently, performing the P1111 diagnostic table may isolate the cause of the fault. |
| • | For an intermittent, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the malfunction is present.
-
If both DTCs P1635 and P1639 are set at the same time, this indicates that the IAT signal circuit is shorted to a voltage.
-
Use the Freeze Frame/Failure Records in order to locate an intermittent condition. This information may help determine how many miles occurred since the DTC set. The Fail Counter and the Pass Counter may help determine the number of ignition cycles that the diagnostic test reported a pass or a fail. In order to isolate under what conditions the DTC failed, operate the vehicle within the same Freeze Frame conditions that you observed. Check the data regarding the following conditions:
-
An IAT above 139°C (282°F) indicates the PCM and IAT sensor wiring is OK.
-
An IAT above 139°C (282°F) indicates the PCM and IAT sensor signal circuit is OK.
-
Disconnecting the PCM allows you to use the DMM in order to test the circuit continuity. This helps to locate an open circuit or a shorted circuit.
-
Disconnecting the PCM allows you to use the DMM in order to test for a short to voltage.
-
This step tests for another circuit that is shorted to the IAT signal circuit.
-
Before you replace the PCM, inspect for proper terminal tension and connections at the PCM harness.
| • | The RPM |
| • | The vehicle load |
| • | The vehicle speed |
| • | The temperature |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
Is the IAT sensor at the specified value? | -39°C (-38°F) | Go to Step 3 | Go to Step 4 | |||||||||
Are DTCs P1635 and P1639 also set? | -- | Go to Step 14 | Go to Step 5 | |||||||||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids | |||||||||
Is the IAT sensor at the specified value? | 140°C (284°F) | Go to Step 8 | Go to Step 6 | |||||||||
Connect the IAT sensor signal circuit with jumper wires to a known good ground. Is the IAT sensor at the specified value? | 140°C (284°F) | Go to Step 10 | Go to Step 7 | |||||||||
Is the IAT sensor signal circuit open? | -- | Go to Step 11 | Go to Step 16 | |||||||||
Does the DMM display a voltage? | -- | Go to Step 14 | Go to Step 9 | |||||||||
Use a DMM in order to test for continuity from the IAT signal circuit to all other PCM circuits at the PCM harness connectors. For example, probe 1 lead to the IAT sensor signal at the PCM harness connector circuit, and probe the other lead to each terminal at the PCM harness connectors. Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity within the specified range from the IAT sensor signal circuit to any other PCM circuit? | 0-2ohms | Go to Step 15 | Go to Step 12 | |||||||||
10 |
Is the low reference circuit of the IAT sensor open? | -- | Go to Step 13 | Go to Step 16 | ||||||||
11 | Repair the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||||||
12 |
Important: Inspect for faulty connections at the IAT harness before replacing the MAF/IAT. Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||||
13 | Repair the low reference circuit of the IAT sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||||||
14 | Repair the IAT sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||||||
15 | Repair the short between the IAT sensor signal circuit and the PCM circuit that had continuity. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||||||
Did you find and repair the condition? | -- | Go to Step 18 | Go to Step 17 | |||||||||
17 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||||
18 |
Does the DTC run and pass? | -- | Go to Step 19 | Go to Step 2 | ||||||||
19 | With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||
