Air Quality Sensor -G238- Functionality, Checking
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 Information.
The Air Quality Sensor -G238- (with Humidity Sensor in Fresh Air Intake Duct -G657-) is only installed on a vehicle with a "High" A/C system. Refer to the Parts Information.
On a vehicle with a "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 Information and the Audi Sales Program.
On a vehicle with a "Low" A/C system (or without an A/C system only a heater) 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 Information and the Audi Sales Program.
Depending on the vehicle version, there are different fresh air intake versions. Depending on the version of the fresh air intake the component location of the Air Quality Sensor -G238- (with the Humidity Sensor in Fresh Air Intake Duct -G657-) -A- is different. Refer to FRESH AIR INTAKE, REMOVING AND INSTALLING . These and the following illustrations show the Air Quality Sensor -G238- (with the Humidity Sensor in Fresh Air Intake Duct -G657-) -A- on a fresh air intake in the version which was installed at the start of production.
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 influences. 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). Use the 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 concern with these components. Refer to Infotainment/MMI Owner's Manual.
Special Tools and Equipment
- Vehicle Diagnostic Tester
- Commercial gas lighter
Test Requirements
- Vehicle standing in clean surrounding air (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.
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.
Function, Checking
So that with the plenum chamber cover -A- installed no water flows via the intake box -B- in the heater and A/C unit, the plenum chamber cover -A- and the outer cover (rain water drain channel) -C- must not be damaged. In addition the plenum chamber cover -A- must be correctly and completely engaged in the lower windshield frame -D-.
So that no foreign objects (for example leaves) enter in the intake box -B- the intake grille must not be damaged. Check it.
Depending on the version, for some countries with high dust levels (for example China), a dust filter is installed in the filter mount instead of the grille. This dust filter prevents pollen and sand from getting sucked into the Fresh Air Blower -V2-.
-- Loosen the right front plenum chamber cover -F- from the vehicle and carefully lift slightly. Refer to PLENUM CHAMBER COVER, REMOVING AND INSTALLING .
-- Turn the Air Quality Sensor -G238- / Humidity Sensor in Fresh Air Intake Duct -G657- -A- approximately 90° and remove it from the mount on the fresh air intake -E- (do not remove the connector -B-).
-- Connect the Vehicle Diagnostic Tester to the diagnostic connection of the vehicle with the ignition switched on and initiate the Guided Fault Finding.
-- Start the engine.
-- Retrieve the Front A/C Display Control Head -E87- DTC memory using the 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. Used the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
For an explanation of the possible displays, use the 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 using the 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 90°.
-- Allow a little bit of gas from the lighter -B- to flow from above on the area -A- of the Air Quality Sensor -G238-.
If the Air Quality Sensor -G238- comes in contact with cigarette smoke or with gas from a lighter, it will react since butane gas is heavier than air; therefore, remove 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. Using the 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.
The sensor itself cannot currently be checked with service equipment, however, if the air composition around the sensor changes, the signal from the Air Quality Sensor -G238- and the display value for the request for the fresh air and recirculating air mode status also changes. Use the 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. Using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
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 system operating condition (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.
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. Use the 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 contaminants. Refer to DUST AND POLLEN FILTER, REMOVING AND INSTALLING .
-- Connect a vehicle diagnostic tester to the diagnostic connection 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. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
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. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
-- Drive the vehicle into an area with a relatively clean surrounding air (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.
Pay attention to the descriptions. Refer to DUST AND POLLEN FILTER, REMOVING AND INSTALLING and Air Quality Sensor -G238- FUNCTION (functionality of the Air Quality Sensor -G238- and the Humidity Sensor In Fresh Air Intake Duct -G657-).