Circuit Description
The Intake Air Temperature (IAT) sensor contains a semiconductor device which changes the resistance based on the temperature (a thermistor). 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 PCM applies 5.0 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 (thermistor) resistance is high. The PCM's signal voltage 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; therefore, the PCM senses a low signal voltage, or a high temperature.
When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0500, P0502, P0503, P1258 not set. |
| • | The engine coolant temperature is greater than 0°C (32°F). |
| • | The vehicle speed is less than 11.0 km/h (7.0 mph). |
| • | The Mass Air Flow is less than 15.0 g/s. |
Conditions for Setting the DTC
| • | The Intake Air Temperature is less than -35°C (-31°F). |
| • | All conditions met for 4.5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Important:
• Remove any debris from the PCM\TAC module connector surfaces before
servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are installed
correctly. The gaskets prevent contaminate intrusion into the PCM\TAC
modules. • For any test that requires probing the PCM or a component
harness connector, use the Connector Test Adapter Kit J 35616
. Using this kit prevents damage
to the harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | The following may cause an intermittent: |
| - | Poor Connections; Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. |
| - | Mis-routed harness |
| - | Rubbed through wire insulation |
| - | Broken wire inside the insulation |
| • | 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 vs 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 Symptoms . |
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 the IAT signal circuit is shorted to a voltage.
-
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.
-
An intake air temperature above 139°C (282°F) indicates the PCM and IAT sensor wiring is OK.
-
An intake air temperature above 139°C (282°F) indicates the PCM and IAT sensor signal circuit is OK.
-
Disconnecting the PCM allows using the DMM in order to test continuity of the circuits. This aids in locating an open or a shorted circuit.
-
Disconnecting the PCM allows using the DMM in order to test for a short to voltage.
-
This step is testing for another circuit shorted to the IAT signal circuit.
-
Inspect for proper terminal tension/connections at the PCM harness before replacing the PCM.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the IAT sensor at the specified value? | -39°C (-38°F) | |||
Are DTCs P1635 and P1639 also set? | -- | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Is the IAT sensor at the specified value? | 140°C (284°F) | |||
Jumper the IAT sensor signal circuit to a known good ground. Is the IAT sensor at the specified value? | 140°C (284°F) | |||
Is the IAT sensor signal circuit open? | -- | |||
Does the DMM display a voltage? | -- | |||
Test for continuity from the IAT signal circuit to all other PCM circuits at the PCM harness connectors using a DMM J 39200 . Example: probe one 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 | |||
10 |
Is the IAT sensor ground circuit open? | -- | ||
11 | Repair the IAT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
12 |
Important: Inspect for poor connections at the IAT harness before replacing the IAT. Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | -- | |
13 | Repair the IAT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
14 | Repair the IAT sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
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? | -- | -- | |
Did you find and repair the condition? | -- | |||
17 |
Important: Program the replacement PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement . Replace the PCM. Is the action complete? | -- | -- | |
18 |
Does the scan tool indicate that this test ran and passed? | -- | ||
19 | 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 |
