For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P009A: Intake Air Temperature (IAT)-Ambient Air Temperature (AAT) Correlation

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
AAT Sensor Signal | P0072 | P0073 | P0073 | P0073 | P009A, P0074
Low Reference | -- | P0073 | P0073 | P0073 | P0074
IAT Sensor Signal | P0112 | P0113 | P0113 | P0113 | P009A, P0111, P0114
Low Reference | -- | P0113 | P0113 | P0113 | P0111, P0114

### Typical Scan Tool Data

#### Ambient Temperature

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The ignition is ON, or the engine is running Parameter Normal Range: Varies with ambient temperature
AAT Sensor Signal | 90°C (194°F) | -40°C (-40°F) | -40°C (-40°F)
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)

#### IAT Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The ignition is ON, or the engine is running Parameter Normal Range: Varies with ambient temperature
IAT Sensor Signal | 129°C (264°F) | -40°C (-40°F) | -40°C (-40°F)
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F)

### Circuit/System Description

The intake air temperature (IAT) sensor is integrated with the mass air flow (MAF) sensor. The IAT sensor is a variable resistor that measures the temperature of the air when it first enters the induction system. The engine control module (ECM) supplies 5 volts to the IAT sensor signal circuit and supplies a ground to the low reference circuit.

The ambient air temperature (AAT) sensor system used on this vehicle consists of two separate sensors mounted in the grille area. The AAT sensors are variable resistors that measure the temperature of the air as it enters the grille opening. This system is uniquely wired as explained by the following:

• | The driver side mounted AAT sensor reports information to the logic module. The logic module supplies 5.8 volts to the sensor signal circuit and a ground for the low reference circuit.

• | The passenger side mounted AAT sensor reports information to the engine control module (ECM). However the circuits for this sensor are first routed and connected to the underhood fuse block. The internal circuitry of the underhood fuse block is a direct pass-through for the circuits that are then routed to the ECM. The ECM supplies 5 volts to the passenger side mounted AAT sensor signal circuit and a ground for the low reference circuit.

The purpose of this diagnostic is to verify the performance of the AAT sensor system by comparing the measured AAT to a modeled AAT, that is derived from the following various inputs:

• | Barometric (BARO) pressure

• | Mass air flow (MAF)

• | Engine speed

• | Engine coolant temperature (ECT)

• | AAT

• | IAT

• | Vehicle speed

### Conditions for Running the DTC

#### P009A

• | DTCs P0068, P0072, P0073, P0074, P0101, P0102, P0103, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0128, P0335, P0340, P0341, P0336, P0365, P0366, P0501, P2227, P2228, P2229 or P2610 are not set.

• | The engine is running.

• | The ignition voltage is greater than 10 volts.

• | The MAF Sensor parameter is between 70-500 kg/h.

• | The ECT Sensor parameter is between 69-120°C (156-248°F).

• | The Engine Speed parameter is between 928-6496 RPM.

• | The vehicle speed is between 35-160 km/h (22-100 mph).

• | The above conditions have been met for greater than 15 seconds.

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P009A

The ECM detects that the AAT sensor signal is not within a calibrated range of the modeled AAT for greater than 2 seconds.

### Action Taken When the DTC Sets

DTC P009A is a Type B DTC.

### Conditions for Clearing the MIL/DTC

DTC P009A is a Type B DTC.

### Diagnostic Aids

• | The AAT sensors respond quickly to temperature changes, however the ECM processes an extremely large number of samples before it updates the information that is sent to the scan tool. An update to the scan tool Ambient Temperature parameter may not occur until the next drive cycle.

• | It is not possible to swing the scan tool Ambient Temperature parameter warm or cold as is usually done with traditional methods of testing when servicing the IAT sensor or the ECT sensor.

• | The resistance of the AAT sensors respond quickly to temperature changes. These changes can be monitored with a DMM. Simply placing the sensor in a refrigerator or freezer, then removing it after several minutes will induce a rapid change in the resistance measurement as it warms up.

• | The AAT sensors are identical and can be exchanged with each other for testing purposes.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information.

### Circuit/System Verification

• | If the ignition has been OFF for 8 hours or greater, the ambient temperature, the IAT and the ECT should be within 9°C (16°F) of each other. Ignition ON, observe the scan tool Ambient Temperature, IAT Sensor and the ECT Sensor parameters. Compare those sensor parameters to each other to determine if the condition is current.

• | If the ECT Sensor parameter and/or the IAT Sensor parameter appears to be inaccurate, measure and record the resistance of the sensors at various ambient temperatures, then compare those measurements to the Temperature Versus Resistance table.

• | Drive the vehicle under various operating conditions. Observe the scan tool Ambient Temperature parameter. The reading should correlate closely to the current ambient temperature.

• | Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Verify that debris is not blocking the airflow through the front of the grille area.
2. Verify that the port of the passenger side AAT sensor is free of debris and contamination.
3. Ignition OFF for 90 seconds, disconnect the harness connector at the passenger side AAT sensor.
4. Test for less than 5 ohms between the low reference circuit and ground.

⇒ | If greater than the specified range, test the low reference circuit for a high resistance. If the circuit tests normal, replace the ECM.

5. Disconnect the ECM.
6. Test the AAT sensor signal circuit for less than 5 ohms.

⇒ | If greater than the specified range, test the signal circuit for a high resistance.

7. If the circuits test normal, test or replace the AAT sensor.

### Component Testing

Allow the sensor to rest on a workbench away from sunlight and any direct heat ore cold source. Connect the DMM to the sensor, and measure the resistance at an ambient temperature of 22-23°C (72-73°F). The resistance should measure between 4.9-5.4K ohms.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup, and programming