For 1990-2009 cars

Schematic Reference: Engine Controls Schematics

### Circuit Description

The Intake Air Temperature (IAT) sensor contains a semiconductor device which changes resistance based on 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 a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine intake air temperature.

When the intake air is cold, the sensor (thermistor) resistance is high, and the PCMs signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the PCM will sense a high signal voltage (low temperature). When the intake air is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense a low signal voltage (high temperature).

When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC will set.

### Conditions for Setting the DTC

• | DTC(s) P0100, P0102, P0103, P0117, P0118, P0500, P0502, P0503 not set.

• | Engine operating longer than 100 seconds.

• | Engine Coolant Temperature greater than 0°C (32°F).

• | Intake Air Temperature is less than -35°C (-31°F).

• | Vehicle speed less than 11 km/h (7 mph).

• | Mass Air Flow less than 15 grams per second.

• | All conditions met for 4.5 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

• | The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

• | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.

• | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | PCM battery voltage is interrupted.

• | Using a Scan tool.

### Diagnostic Aids

• | An intermittent may be caused by the following:

- | Mis-routed harness.

- | Rubbed through wire insulation.

- | Broken wire inside the insulation.

• | If other DTCs are set that share the same ground and/or 5.0 volt reference circuit, check for faulty connections and for faulty wiring.

• | If the engine has been allowed to sit overnight, the engine coolant temperature and 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 it is determined that the DTC occurs intermittently, performing the P1111 diagnostic table may isolate the cause of the fault.

For intermittents, refer to Symptoms .

### Test Description

Number(s) below refer to step numbers on the diagnostic table.

1. Determines if the malfunction is present. For any test that requires probing the PCM or component harness connectors, must use the Connector Test Adapter Kit J 35616-A. Using this kit will prevent any damage to the harness connector terminals.

2. Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.

3. If the intake air temperature goes above 150°C (302°F), indicates the PCM and IAT wiring are OK.

4. If the intake air temperature goes above 150°C (302°F), indicates the PCM and IAT signal circuit is OK.

5. Disconnecting the PCM will allow using the DVM (J 39200) to check continuity of the circuits. This will aid in locating an open or shorted circuit.

6. Disconnecting the PCM will allow using the DVM (J 39200) to check continuity of the circuits. This will aid in locating an open or shorted circuit.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install the scan tool.
2. Turn the ignition ON, engine OFF.
3. Monitor the IAT display on the Engine 1 Data List of the scan tool.

Is the IAT at the specified value?

-40°C (-40°F)

Go to Step 4

Go to Step 3

3 |

1. Turn the ignition ON, engine OFF, review Freeze Frame and/or Failure Records data for this DTC and note parameters.
2. Turn the ignition OFF for 15 seconds.
3. Start the engine and operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame/Failure Records as possible. Special operating conditions that need to be met before the PCM will run this diagnostic, where applicable, are listed in Conditions for Setting the DTC.
4. Using the scan tool, select DTC, Specific, then enter the DTC number which was set.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Disconnect the IAT Sensor electrical connector.
2. Jumper the IAT harness terminals together.
3. Observe IAT parameter on the scan tool.

Is the IAT at the specified value?

151°C (304°F)

Go to Step 9

Go to Step 5

5 | Jumper the IAT signal circuit to a known good ground. Is the IAT at the specified value? | 151°C (304°F) | Go to Step 8 | Go to Step 6
6 |

1. Turn the ignition OFF.
2. Disconnect the PCM electrical connectors.
3. Check the IAT sensor signal circuit for an open.

Is the IAT sensor signal circuit open?

--

Go to Step 7

Go to Step 11

7 | Repair the IAT sensor signal circuit. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | Go to Step 12 | --
8 |

1. Turn the ignition OFF.
2. Disconnect the PCM electrical connectors.
3. Check the IAT sensor ground circuit for an open.

Is the IAT sensor ground circuit open?

--

Go to Step 10

Go to Step 11

9 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 12 | --
10 | Repair the IAT sensor ground circuit. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | Go to Step 12 | --
11 | Important:: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | Go to Step 12 | --
12 |

1. Using the scan tool, select DTC, Clear Info.
2. Start the engine and idle at normal operating temperature.
3. Select DTC, Specific, then enter the DTC number which was set.
4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 13

Go to Step 2

13 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK