Audi Q7: Air Quality Sensor -G238- Function

Function of Air Quality Sensor -G238-

  Note

• There are different versions of the Air Quality Sensor -G238-/ humidity sensor in Fresh Air Intake Duct -G657--A-. Therefore, ensure the correct allocation. Refer to the Parts Catalog.
• Depending on the vehicle version, there are different fresh air intake versions. Refer to the Parts Catalog. Depending on the version of the fresh air intake the component location of the Air Quality Sensor -G238--C- (with the humidity sensor in Fresh Air Intake Duct -G657--D-) is different. Refer to → Chapter "Fresh Air Intake, Removing and Installing". This and the following illustrations show the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) for a fresh air intake version "1".
• On a vehicle with a "Mix" of "High" A/C system a sensor -A- is installed in which the Air Quality Sensor -G238--C- with the Humidity Sensor in Fresh Air Intake Duct -G657--D- are combined in a single component. Refer to the Parts Catalog and the Audi Sales Program.
• On a vehicle with a "Low" or "Mid" A/C system only a sensor -A- with a Humidity Sensor in Fresh Air Intake Duct -G657--D- but without an Air Quality Sensor -G238--C- is installed. Refer to the Parts Catalog and the Audi Sales Program.
• The Air Quality Sensor -G238--C- uses a sensor to determine the NOx level (nitrogen oxide) and CO level (carbon monoxide) in the air flowing by and exchanges this information with the Front A/C Display Control Head -E87- via a local data bus. Therefore, ensure the proper version and allocation of the Air Quality Sensor -G238- / humidity sensor in Fresh Air Intake Duct -G657-. Refer to the Parts Catalog.
• The measured value of the Air Quality Sensor -G238--C- is evaluated by the Front A/C Display Control Head -E87-. Upon request, the Front A/C Display Control Head -E87- switches to recirculating air mode if no shut-off condition is present. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• Certain A/C system functions (for example, control of automatic recirculation mode) can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"vehicle" menu. The A/C system control can also be influenced via the presets in the MMI (Multi Media Interface) under the "A/C system" function in the "Car"/"Vehicle" menu. Therefore, check the preset in the MMI first in the case there is a problem with these components. Refer to Infotainment/MMI Operating Instructions.
• The Air Quality Sensor -G238--C- requires approximately 30 seconds to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the Air Quality Sensor -G238- is limited.
• The Air Quality Sensor -G238--C- detects pollutants in the surrounding air (usually gasoline and/or diesel exhaust) and causes the Front A/C Display Control Head -E87- to switch the A/C system to recirculation mode.

The Front A/C Display Control Head -E87- identifies the type and intensity of the air pollutant by the signal from the Air Quality Sensor -G238-. Moreover, the Front A/C Display Control Head -E87- receives the sensitivity set by the Multimedia System Control Head -E380- via the data bus. Based on this information, the Front A/C Display Control Head -E87- then determines if and when the A/C system switches to recirculating air mode. Refer to the Infotainment/MMI Operating Instructions and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Example:

- At an outside temperature above approximately +2 ºC (35.6 ºF), the recirculation mode is switched on upon request from the Air Quality Sensor -G238- when there is only a slight increase in the pollutants in the ambient air.

- If the outside air temperature goes below -1ºC (30.2 ºF) and "ECON mode" is activated (the A/C compressor is switched off and the indicator lamp in the A/C Max or A/C button is off), the switch-over takes place first when there is a significant increase in the pollutant concentration and only for approx. 15 seconds. If there is another increase in the pollutant concentration within approximately two minutes, the Front A/C Display Control Head -E87- does not switch to "recirculation mode" at this time.

- If the A/C compressor is switched off ("ECON" mode is on and the indicator lamp in the A/C Max or A/C button is off), the maximum duration of the "automatic recirculation mode" is limited to 15 seconds by the Front A/C Display Control Head -E87- (so that the windshield, rear window, and door windows do not fog up).

- If the concentration decreases, the A/C system switches to the fresh air mode.

- The duration of "automatic recirculating air mode" depends on the version of the Front A/C Display Control Head -E87- and the setting on the Multimedia System Control Head -E380-. If the outside air temperature is below +10 ºC (50 ºF) and the maximum sensitivity on the Multimedia System Control Head -E380- is reached, the system will stay on for approximately 30 seconds in "automatic recirculation mode". After this, it switches back to fresh air mode. If another increase in the pollutant concentration occurs within approximately two minutes, the Front A/C Display Control Head -E87- does not switch over to "automatic recirculation mode" during this time.

• The "automatic recirculating air mode" function can be switched off at any time. If the function is active, the A/C compressor is switched on with a request for "automatic recirculating air mode" and also when the exterior temperature is below approximately +2 ºC (35.6 ºF). If the temperature is below -5 ºC (23 ºF), then it is not possible to use the A/C compressor.
• At setting "automatic recirculating air mode" in the MMI (Multi Media Interface), the A/C compressor can also be switched on when the recirculating air mode is manually switched on (using the "recirculation button") up to a temperature of approximately - 5ºC (23 ºF).

• To ensure that the A/C system is not constantly working in recirculating air mode in areas with consistently high air pollution, the Air Quality Sensor -G238- is self-adapting (it adjusts its sensitivity to the environmental conditions).
• If the outside air pollution load remains relatively high for a long period of time, the Air Quality Sensor -G238- starts to adapt itself to the altered environmental conditions through an adaptation program so that the air recirculation request is generally shorter than 12 minutes in uniformly polluted surrounding air. If a succession of peaks in the polluted air is detected, the A/C system can operate over a longer period of time in recirculating air mode.
• A certain amount of time is required for repositioning of the A/C system doors. In the event that a sudden increase in pollutants is encountered (for example when driving through a diesel exhaust cloud) gaseous pollutants can be taken in with the fresh air into the passenger compartment until the door can be closed. For this reason, on vehicles equipped with an Air Quality Sensor -G238- a dust and pollen filter is installed with a charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced.
• To prevent excessive operation of the back pressure/fresh air door and the air recirculation door, the door is not immediately activated if there is a nominal increase in pollutants in the surrounding air (the Air Quality Sensor -G238- does not send a request to the Front A/C Display Control Head -E87-). The filtering of the activated charcoal insert in the dust and pollen filter will be sufficient.
• In order to avoid excessive operation of the back pressure/fresh air door and the air recirculation door, a request from the Air Quality Sensor -G238- for "automatic recirculation mode" remains active for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that recirculation mode is no longer necessary.
• To defog fogged-up windshield, rear window, and door windows as quickly as possible, the Front A/C Display Control Head -E87- does not allow recirculation mode in the "defrost" mode (a request from the Air Quality Sensor -G238- is not implemented).
• After the ignition is switched on, Air Quality Sensor -G238- requires approximately 30 seconds to be operational (warm-up time). During this time there is no request from the Air Quality Sensor -G238- to the Front A/C Display Control Head -E87- for the "automatic recirculating air mode".
• Sensor -A- (combination sensor with the Air Quality Sensor -G238- and the Humidity Sensor in Fresh Air Intake Duct -G657-) is a highly sensitive electronic component that can be damaged if it comes in direct contact with fluids, solvents, fuels and certain chemical compounds. Moreover, the function of the Humidity Sensor in Fresh Air Intake Duct -G657- can be severely affected by direct contact with water so that correct moisture values can no longer be measured (briefly or permanently depending on the composition of the fluid). For this reason, do not install sensors that may have come into contact with these substances.

• Under certain ambient influences, when switching on the ignition (for example, when the air pollution is high), if a fault on the Air Quality Sensor -G238- is stored in the Front A/C Display Control Head -E87- during the Air Quality Sensor -G238- warm-up time, even though the sensor is OK, proceed as follows:

- Switch off the ignition for a minimum of two minutes.

- Switch on the ignition and wait at least two minutes.

- Read the DTC memory of the Front A/C Display Control Head -E87-. If the Air Quality Sensor -G238- still displays a static malfunction, perform Guided Fault Finding. Refer to Vehicle Diagnostic Tester. If the Air Quality Sensor -G238- is no longer displayed as a malfunction, or the malfunction was sporadic, the Air Quality Sensor -G238- is OK (and does not need to be observed). Erase the event memory.

Air Quality Sensor -G238- Functionality, Checking

  Note

• There are different versions of the Air Quality Sensor -G238-/ Humidity Sensor in Fresh Air Intake Duct -G657--A-. Therefore, ensure the correct allocation. Refer to the Parts Catalog.
• Depending on the vehicle version, there are different fresh air intake versions. Refer to the Parts Catalog. Depending on the version of the fresh air intake the component location of the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) is different. Refer to → Chapter "Fresh Air Intake, Removing and Installing". This and the following illustrations show the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) for a fresh air intake version "1".
• On a vehicle with a "Mix" of "High" A/C system a sensor -A- is installed in which the Air Quality Sensor -G238--C- with the Humidity Sensor in Fresh Air Intake Duct -G657--D- are combined in a single component. Refer to the Parts Catalog and the Audi Sales Program.
• On a vehicle with a "Low" or "Mid" A/C system only a sensor -A- with a Humidity Sensor in Fresh Air Intake Duct -G657--D- but without an Air Quality Sensor -G238--C- is installed. Refer to the Parts Catalog and the Audi Sales Program.
• The Air Quality Sensor -G238--A- requires approximately 30 seconds to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the Air Quality Sensor -G238- is limited.
• During the warm-up phase, the Air Quality Sensor -G238- malfunctions may occur under certain ambient conditions. Only replace the Air Quality Sensor -G238- if the Air Quality Sensor -G238- is continually registered as faulty. If the malfunction indicator for the Air Quality Sensor -G238- changes from "static" to "sporadic" after switching the ignition off and back on again (wait at least two minutes), the Air Quality Sensor -G238- is OK and it is no longer necessary to pay attention to the DTC memory entry (erase the DTC memory). Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• Certain A/C system functions (for example, control of automatic recirculation mode) can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"vehicle" menu. The A/C system control can also be influenced via the presets in the MMI (Multi Media Interface) under the "A/C system" function in the "Car"/"Vehicle" menu. Therefore, check the preset in the MMI first in the case there is a problem with these components. Refer to Infotainment/MMI Operating Instructions.

Special Tools and Equipment

• Vehicle diagnostic tester

Test Requirements

• Vehicle standing in a clean atmosphere (away from running engines, exhaust vents, etc.)
• Engine compartment and the plenum chamber are clean (not contaminated with oil or fuel)
• The engine compartment and the plenum chamber were not sprayed with cleaning agents or preservatives containing solvents
• "Automatic recirculating air mode" is switched on.

  Note

It is possible to switch the "automatic recirculation mode" on or off via the "A/C" function in the "car"/"vehicle" menu in the MMI (Multi Media Interface). Refer to Infotainment/MMI operating instructions.

Checking Function

- Remove the plenum chamber cover. Refer to → Body Interior; Rep. Gr.50; Bulkhead; Plenum Chamber Cover, Removing and Installing.

  Note

So that with an installed plenum chamber cover no water runs via the outer fresh air intake box cover (rain water drain channel) -E- in the fresh air intake, the plenum chamber cover must not be damaged. In addition the plenum chamber cover must be correctly and completely engaged in the windshield frame.

- Remove the outer cover for the fresh air intake box (rain water drain channel) -E-. Refer to → Chapter "Fresh Air Intake, Removing and Installing"

- Remove the Air Quality Sensor -G238- / Humidity Sensor in Fresh Air Intake Duct -G657--A- from the inner cover for the fresh air intake box -F- (do not remove connector -B-).

- Connect the Vehicle Diagnostic Tester to the data link connector of the vehicle with the ignition switched on and initiate the Guided Fault Finding. Refer to Vehicle Diagnostic Tester.

- Start the engine.

- Retrieve the Front A/C Display Control Head -E87- DTC memory. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Set the "Auto" mode on the Front A/C Display Control Head -E87-.

- Set "automatic recirculating air mode" via the MMI (Multi Media Interface) in the Front A/C Display Control Head -E87-. Refer to Infotainment/MMI Operating Instructions.

- Wait two minutes. (Air Quality Sensor -G238- warm-up time).

- Via the Vehicle Diagnostic Tester select the "Read the measured values" function and read out the current status for the fresh or recirculating air mode. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

  Note

• For an explanation of the possible displays. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The Front A/C Display Control Head -E87- calculates the measured values of the Air Quality Sensor -G238- (for the air pollution) and the different settings of the status for the recirculating or fresh air mode. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Specified value:

• The heating and A/C system works in fresh air mode.

- Turn the Air Quality Sensor -G238--A- approximately 90º.

- Allow a little bit of gas -B- to flow past from the top area -A- of the Air Quality Sensor -G238-.

- In the Guided Fault Finding function "Read the measured values" read out the current status of the fresh or recirculating air mode. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Specified Values:

• In the display fields, the measured values for the "fresh air/recirculating air mode" change with respect to the initial value, thus indicating that the Air Quality Sensor -G238- is functioning properly and the Air Quality Sensor -G238- electronics are evaluating the measured values correctly.
• The display field will show that the heating and A/C system is working in the recirculating air mode.

  Note

The sensor itself cannot be checked with service equipment at this time, if the air composition around the sensor changes, the signal from the Air Quality Sensor -G238- and also the display value from the request for the fresh and recirculating air mode status also changes. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Wait a short period of time (approximately one minute, depending on amount of test gas flowing at the sensor).

- In the Guided Fault Finding function "Read the measured values" read out the current status of the fresh or recirculating air mode. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

  Note

Due to changed pollution values, it is possible that different values can be displayed than those by the first measuring.

- Read the display with the measured values for the A/C operating status (recirculation/fresh air operation).

Specified value:

• The display field will show that the heating and A/C system is working in the fresh air mode.

  Note

• If a value deviating from the "fresh air mode" is displayed in the "read measured values" function of the Guided Fault Finding, there is already a request for recirculation mode (for example, due to the request for "maximum cooling output" or the "manual recirculation mode" setting). Select an operating mode that does not require recirculation mode.
• If it is displayed in the "read measured values" function of the Guided Fault Finding that the Air Quality Sensor -G238- is already requesting automatic recirculation mode, clean the plenum chamber or move the vehicle into an area where the air is cleaner. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

If the Function of Air Quality Sensor -G238- is OK for This Test and There is a Customer Complaint Continue as Follows:

- Check the dust and pollen filter for soiling. Refer to → Chapter "Dust and Pollen Filter, Removing and Installing".

- Connect a Vehicle Diagnostic Tester to the data link connector of the vehicle with the ignition switched on and initiate the Guided Fault Finding. Refer to Vehicle Diagnostic Tester.

- Via the Vehicle Diagnostic Tester, select the "read measured values" function. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

  Note

A second technician is required to read out the displayed values while driving.

Note Safety Information:

- Read out the displays in the "read measured values" function of the Guided Fault Finding for the measured values of the Air Quality Sensor -G238- and the recirculation/fresh air mode request. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Drive the vehicle into an area with a relatively clean atmosphere (system in fresh-air mode).

- Then drive the vehicle into an area where the surrounding air is polluted (for example, onto an uphill road with truck traffic).

- Read the displays in the different display fields. The displays in the different display fields must change; for example, when driving through a diesel exhaust cloud.

  Note

Pay attention to the descriptions. Refer to → Chapter "Dust and Pollen Filter, Removing and Installing" and → Chapter "Air Quality Sensor -G238- Function" (functionality of the Air Quality Sensor -G238- and the Humidity Sensor In Fresh Air Intake Duct -G657-).

Humidity Sensor In Fresh Air Intake Duct -G657- Function

  Note

• There are different versions of the Air Quality Sensor -G238-/ Humidity Sensor in Fresh Air Intake Duct -G657--A-. Therefore, ensure the correct allocation. Refer to the Parts Catalog.
• Depending on the vehicle version, there are different fresh air intake versions. Refer to the Parts Catalog. Depending on the version of the fresh air intake the component location of the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) is different. Refer to → Chapter "Fresh Air Intake, Removing and Installing". This and the following illustrations show the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) for a fresh air intake version "1".
• On a vehicle with a "Mix" of "High" A/C system a sensor -A- is installed in which the Air Quality Sensor -G238--C- with the humidity sensor in Fresh Air Intake Duct -G657--D- are combined in a single component. Refer to the Parts Catalog and the Audi Sales Program.
• On a vehicle with a "Low" or "Mid" A/C system only a sensor -A- with a Humidity Sensor in Fresh Air Intake Duct -G657--D- but without an Air Quality Sensor -G238--C- is installed. Refer to the Parts Catalog and the Audi Sales Program.

• The sensor of the Humidity Sensor in Fresh Air Intake Duct -G657--D- installed in the sensor -A- calculates the temperature and the moisture in the air flowing by and exchanges the information with the Front A/C Display Control Head -E87- via the local data bus. Therefore, ensure the proper version of the Air Quality Sensor -G238- / humidity sensor in Fresh Air Intake Duct -G657-. Refer to the Parts Catalog.
• The measured value of the Humidity Sensor in Fresh Air Intake Duct -G657- is evaluated by the Front A/C Display Control Head -E87-.
• Certain A/C system functions (for example, control of automatic recirculation mode) can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"vehicle" menu. The A/C system control can also be influenced via the presets in the MMI (Multi Media Interface) under the "A/C system" function in the "Car"/"Vehicle" menu. Therefore, check the preset in the MMI first in the case there is a problem with these components. Refer to Infotainment/MMI Operating Instructions.
• The Front A/C Display Control Head -E87- uses the measured values to calculate the current relative humidity of the drawn-in fresh air. The calculated humidity value is used to detect whether there is a risk of the windshield, rear window, and door windows fogging up on the inside. If that is the case, the Front A/C Display Control Head -E87- changes various characteristic curves to counteract this. This can be performed, for example, by lowering the evaporator temperature (by activating the A/C compressor), by raising the response thresholds for the request for automatic recirculation mode, by preventing motor shut-off via the start-stop function, etc. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The Humidity Sensor in Fresh Air intake Duct -G657- needs approximately 30 seconds until it has reached its operating temperature after the ignition is switched on. During the warm-up phase, the function of the Humidity Sensor in Fresh Air intake Duct -G657- is limited.
• Sensor -A- (combination sensor with the Air Quality Sensor -G238- and the Humidity Sensor in Fresh Air Intake Duct -G657-) is a highly sensitive electronic component that can be damaged if it comes in direct contact with fluids, solvents, fuels and certain chemical compounds. Moreover, the function of the humidity sensor in Fresh Air Intake Duct -G657- can be severely affected by direct contact with water so that correct moisture values can no longer be measured (briefly or permanently depending on the composition of the fluid). For this reason, do not install sensors that may have come into contact with these substances.

Humidity Sensor in Fresh Air intake Duct -G657-, Checking

  Note

• There are different versions of the Air Quality Sensor -G238-/ Humidity Sensor in Fresh Air Intake Duct -G657--A-. Therefore, ensure the correct allocation. Refer to the Parts Catalog.
• Depending on the vehicle version, there are different fresh air intake versions. Refer to the Parts Catalog. Depending on the version of the fresh air intake the component location of the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) is different. Refer to → Chapter "Fresh Air Intake, Removing and Installing". This and the following illustrations show the Air Quality Sensor -G238--C- (with the Humidity Sensor in Fresh Air Intake Duct -G657--D-) for a fresh air intake version "1".
• On a vehicle with a "Mix" of "High" A/C system a sensor -A- is installed in which the Air Quality Sensor -G238--C- with the Humidity Sensor in Fresh Air Intake Duct -G657--D- are combined in a single component. Refer to the Parts Catalog and the Audi Sales Program.
• On a vehicle with a "Low" or "Mid" A/C system only a sensor -A- with a Humidity Sensor in Fresh Air Intake Duct -G657--D- but without an Air Quality Sensor -G238--C- is installed. Refer to the Parts Catalog and the Audi Sales Program.
• The Humidity Sensor In Fresh Air Intake Duct -G657--D- requires approximately 30 seconds to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the Humidity Sensor in Fresh Air Intake Duct -G657- is limited. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• The function of the Humidity Sensor in Fresh Air intake Duct -G657- can only be checked via the Guided Fault Finding. The measured values of the Humidity Sensor in Fresh Air intake Duct -G657- are evaluated there via the "read measured values" function and are compared to the temperature and humidity measured at the component location of the Humidity Sensor in Fresh Air intake Duct -G657-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function

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