Circuit Description
The intake air temperature (IAT) sensor contains a thermistor which changes the resistance based on the temperature. The IAT sensor is located in the air intake passage of the engine air induction system. The IAT sensor has a signal circuit and a ground circuit. The powertrain control module (PCM) applies 5 volts on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine intake air temperature.
When the intake air is cold, the sensor resistance is high. The PCM's signal voltage is only pulled down a small amount through the sensor to ground. The PCM senses a high signal voltage, indicating a low temperature. When the intake air is warm, the sensor resistance is low. The signal voltage is pulled down more. The PCM senses a low signal voltage, indicating a high temperature.
When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0117, P0118, P0125, 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 (MAF) is less than 15 g/s. |
| • | The engine run time is more than 100 seconds. |
Conditions for Setting the DTC
| • | The intake air temperature is less than -35°C (-31°F). |
| • | All conditions exist for more than 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:
• Remove any debris from the PCM connector surfaces before servicing
the PCM. Inspect the PCM connector gaskets when you diagnose or replace the
PCM. Ensure that the gaskets are installed correctly. The gaskets
prevent contaminant intrusion into the PCM. • For any test that requires probing the PCM or component
harness connectors, use theJ 35616
connector test adapter kit. Using this kit prevents any
damage to the harness connector terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
If the engine has sat overnight, the engine coolant temperature and the intake air temperature 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. If a short to a separate 5-volt source occurs on the IAT signal circuit, this DTC may set. If this is found to be the problem, a continuity test to all other PCM circuits will be necessary to diagnose the specific circuit. Refer to DTC P1111 .
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 DTC P1635 and DTC P1639 set at the same time, the signal circuit is shorted to a voltage.
-
Using the Freeze Frame/Failure Records may help to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/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 or a fail. In order to isolate when the DTC failed, operate the vehicle within the same Freeze Frame conditions that you observed. These conditions include the following:
-
An intake air temperature above 139°C (282°F) indicates that the PCM and the IAT sensor wiring is OK.
-
An intake air temperature above 139°C (282°F) indicates that the PCM and the IAT sensor signal circuit is OK.
-
Disconnecting the PCM allows you to use the DMM in order to test the continuity of the circuits. This procedure 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.
| • | The RPM |
| • | The vehicle speed |
| • | The vehicle load |
| • | 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 | |
Jumper the IAT sensor signal circuit 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 | |
9 | Test continuity from the IAT signal circuit to all other PCM circuits at the PCM harness connectors using the DMM. Example: probe one lead to the IAT sensor signal circuit at the PCM harness connector, 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? | 0-2 ohms | Go to Step 15 | Go to Step 12 |
10 |
Is the IAT sensor low reference circuit open? | -- | Go to Step 13 | Go to Step 16 |
11 | Repair the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems . Is the action complete? | -- | Go to Step 18 | -- |
12 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 18 | -- |
13 | Repair the IAT sensor low reference circuit. Refer to Wiring Repairs in Wiring Systems . Is the action complete? | -- | Go to Step 18 | -- |
14 | Repair the IAT sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems . Is the action complete? | -- | 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 . Is the action complete? | -- | Go to Step 18 | -- |
16 |
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 . Is the action complete? | -- | 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, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
