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Old 07-19-2014, 05:14 PM   #1
amciver15
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2008 Astra XR
Default CEL P0073 Ambient Air Temp Sensor

Hey everyone,

I've been a long time follower to this forum, first time poster. Owned my 3DR Astra XR since '08, love everything about it. Couple of quirks here and there, coil pack, side mirrors falling off - you know, the usual.

Yesterday, my check engine light came on, ran my OBD scanner and came back with P0073 Ambient Air Temp sensor Circuit High input. I've been trying to figure out how to correct this issue and am having a hard time finding information.

Has anyone else had this error code? What can be done to correct this?

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Old 07-23-2014, 09:14 AM   #2
Astra08
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2008 Astra XR
Default Re: CEL P0073 Ambient Air Temp Sensor

Hopefully this will provide some help:



-----------------------------------------
P0073


DTC P0072-P0074

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection\Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
Review Strategy Based Diagnosis (See: Testing and Inspection\Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
Diagnostic Procedure Instructions (See: Testing and Inspection\Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptors
DTC P0072

Ambient Air Temperature (AAT) Sensor Circuit Low Voltage

DTC P0073

Ambient Air Temperature (AAT) Sensor Circuit High Voltage

DTC P0074

Ambient Air Temperature (AAT) Sensor Circuit Intermittent

Diagnostic Fault Information



Typical Scan Tool Data



Circuit/System Description

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 reports information to the body control module (BCM). The BCM supplies 5.8 volts to the sensor signal circuit and a ground for the low reference circuit.
The passenger side mounted AAT reports information to the engine control module (ECM). However the circuits for this sensor are first routed and connected to the BCM. The internal circuitry of the BCM 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.

Conditions for Running the DTC

P0072

The ignition is ON or the engine is running.
The ignition voltage is greater than 9 volts.
This DTC runs continuously within the enabling conditions.

P0073

The ignition is ON or the engine is running.
The ignition voltage is greater than 9 volts.
This DTC runs continuously within the enabling conditions.

P0074

DTCs P009A, P0072, or P0073 is not set.
The engine is running for greater than 30 seconds.
The ignition voltage is greater than 9 volts.
The vehicle speed is greater than 21 km/h (13 mph).
This DTC runs continuously within the enabling conditions.

Conditions for Setting the DTC

P0072

The ECM detects that the AAT sensor signal is less than 0.5 volts, which is warmer than 90C (194F) for greater than 2 seconds.

P0073

The ECM detects that the AAT sensor signal is more than 4.90 volts, which is colder than -39C (-38F) for greater than 2 seconds.

P0074

The ECM detects that the vehicle is moving and the measured AAT is not within a calibrated range of the modeled AAT for greater than 2 seconds.

Action Taken When the DTC Sets

DTCs P0072, P0073, P0074 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0072, P0073, P0074 are Type B DTCs.

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 intake air temperature (IAT) sensor or the engine coolant temperature (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 and 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 (See: Powertrain Management\Diagrams\Electrical)
Connector End View Reference

Component Connector End Views (See: Diagrams\Connector Views)
Electrical Information Reference

Circuit Testing (See: Testing and Inspection\Component Tests and General Diagnostics)
Connector Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)
Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection\Component Tests and General Diagnostics)
Wiring Repairs (See: Testing and Inspection\Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (See: Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (See: Testing and Inspection\Programming and Relearning) 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 9C (16F) 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.
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

Verify that debris is not blocking the airflow through the front of the grille area.
Verify that the port of the sensor is free of debris and contamination.
Ignition OFF, disconnect the harness connector at the passenger side AAT sensor.
Ignition OFF for 90 seconds, 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 an open/high resistance. If the circuit tests normal, replace the ECM.

Ignition ON, test for 4.8-5.2 volts between the AAT sensor signal circuit and ground.

If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

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 or cold source. Connect the DMM to the sensor, and measure the resistance at an ambient temperature of 22-23C (72-73F). The resistance should measure between 4.9-5.4K ohms.

Repair Instructions

Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.

Control Module References (See: Testing and Inspection\Programming and Relearning) for ECM replacement, setup, and programming

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Old 04-06-2015, 11:59 AM   #3
stimpy29
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Default Re: CEL P0073 Ambient Air Temp Sensor

This is all excellent information. My '08 Saturn Astra recently kicked out the same code. I'd like to replace the sensor on my own, but cannot find a location or picture of where I can find it. I've read that it is behind the grill, but I've looked and just can't seem to locate it.

Any assistance that can be provided would be extremely helpful.

Thank you.
JD

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Old 04-06-2015, 12:04 PM   #4
amciver15
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2008 Astra XR
Default Re: CEL P0073 Ambient Air Temp Sensor

Hey JD,

The issue I posted above was actually corrected by making sure the harness (for fog lights and temp sensors) is properly connected. The sensors are located on the lower grille in the bumper if I'm not mistaken.

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Old 04-06-2015, 03:00 PM   #5
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Default Re: CEL P0073 Ambient Air Temp Sensor

This was extremely helpful. Thank you. I'm working on testing it right now. Hope I can get it sorted out.

JD

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Old 04-06-2015, 04:53 PM   #6
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Default Re: CEL P0073 Ambient Air Temp Sensor

Quick update, it was actually the sensor, replaced it, the code cleared and the car is back to normal. Thanks again for the information and the great people sharing their information. FYI, it was the sensor on the driver's side that was replaced.

JD

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