Air Quality Sensor -G238-, CHECKING
Special tools and workshop equipment required
- Vehicle Diagnostic Tester
- Commercial gas lighter
The Air Quality Sensor -G238- and the Humidity Sensor in Fresh Air Intake Duct -G657- are only installed on a "Convenience" A/C system version (on an automatic climate control system).
For vehicles with a "Basic" A/C system version, neither an Air Quality Sensor -G238- nor a Humidity Sensor in Fresh Air Intake Duct -G657- is installed.
The Humidity Sensor in Fresh Air Intake Duct -G657- -item 1- and the Air Quality Sensor -G238- -item 3- are integrated in the housing -2- on a "Convenience" A/C system version (on an automatic climate control system).
The Air Quality Sensor -G238- -item 3- requires a short period of time to reach its operating temperature after the ignition is switched on.
During the warm-up phase, function is limited and may lead to an error message 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 (such as the regulation of the "automatic recirculating air mode") can be switched on and off via the Multimedia System Control Head -E380-. These settings appear in the instrument cluster center display. Therefore, first check the preset for the "automatic recirculating air mode" if there is a complaint. Refer to the Owner's Manual.
The "automatic recirculating air mode" function is activated when the Air Quality Sensor -G238- (assembled together with the Humidity Sensor in Fresh Air Intake Duct -G657- in one component) detects polluted surrounding air and automatic recirculating air mode is switched on via the Multimedia System Control Head -E380-. The selected or changed functions are shown in the instrument cluster center display. Refer to the Owner's Manual.
The "automatic recirculating air mode" function is switched off when the "defrost mode" function is selected via the Defrost Button -E782-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding " function. For additional information, refer to the Owner's Manual.
Test Requirements
- Vehicle standing in an area with clean surrounding air, away from running engines, exhaust vents, etc.
- Engine compartment and the plenum chamber are clean: Not contaminated with oil or fuel.
- Engine compartment and plenum chamber were not sprayed with cleaning agents or preservatives containing solvents
- "Automatic recirculating air mode" function is switched on.
The "automatic recirculating air mode" function can be switched on and off via the Multimedia System Control Head -E380-. These settings appear in the instrument cluster center display. Refer to the Owner's Manual.
Function, Checking
-- Remove the Air Quality Sensor -G238-. The connector remains connected. Refer to Air Quality Sensor -G238- /Humidity Sensor In Fresh Air Intake Duct -G657-, REMOVING AND INSTALLING .
-- Start the engine.
-- Select "Auto" mode on the Front A/C Display Control Head 3 - E776-.
-- Select the "automatic recirculating air mode" in the Climatronic Control Module -J255- via the Multimedia System Control Head -E380-. Refer to the Owner's Manual.
- The Air Quality Sensor -G238- is operational after approximately two minutes warm-up time.
-- Check the DTC memory of the Climatronic Control Module -J255- and select the "Read measured values" function using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
-- Read out the current status for the fresh air or recirculating air mode via the "read measured values" function. Use 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 Climatronic Control Module -J255- 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.
- The heating and A/C system works in fresh air mode.
-- 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 gas from a lighter, it will react. Gas from a lighter is heavier than air, therefore remove the Air Quality Sensor -G238- and expose it to the gas from above.
-- "Read the measured values" for the fresh air or recirculating air mode status (considering the measured value for the Air Quality Sensor -G238-). Use the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
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).
-- "Read the measured values" for the Air Quality Sensor -G238-.
- Specified value: The measured values return to the initial values in the display fields, thus indicating that both sensors are working correctly, and that the sensor electronics are evaluating the measured values correctly.
Due to changed pollution values, it is possible that different values can be displayed than those by the first measuring.
-- "Read the measured value" for the "recirculating/fresh air mode" operating status of the A/C system.
- Specified value: The display field shows that the A/C system is working in fresh air mode.
If a value deviating from the "fresh air mode" is displayed in the "read measured values" function, there is already a request for recirculating air mode (for example, because of the request for "maximum cooling output" or the "manual recirculating air mode" setting). Select a mode that does not require recirculating air mode.
If it is shown in the "Read measured values" function that the Air Quality Sensor -G238- is already requesting "automatic recirculating air mode", clean the plenum chamber if necessary or move the vehicle into an area where the surrounding air is cleaner.
-- Allow a little bit of gas from the lighter -B- to flow from above on the area -A- of the Air Quality Sensor -G238-.
-- "Read the measured values" for the Air Quality Sensor -G238- on the Vehicle Diagnostic Tester.
-- "Read the measured value" for the "recirculating/fresh air mode" operating status of the A/C system.
- Specified values: There is a request for recirculating air mode and the A/C system is working in recirculating air mode.
If it is shown in the "read measured values" function that the Air Quality Sensor -G238- is requesting "automatic recirculating air mode", but the request cannot be implemented due to a shut-off condition from the Climatronic Control Module -J255-, eliminate the cause of this shut-off condition if necessary.
To prevent frequent operation of the back pressure/fresh air and recirculation doors, the request from the Air Quality Sensor -G238- for "automatic recirculating air mode" remains active for at least 25 seconds (minimum duration period), even if the pollutant concentration in the air has reduced so much that recirculating air mode would no longer be necessary.
-- Wait a short period of time (approximately one minute, depending on amount of test gas flowing at the sensor).
- Specified value: There is no longer a request for recirculating air mode, and the A/C system is working again in fresh air mode.
-- Install the Air Quality Sensor -G238-. Refer to Air Quality Sensor -G238- /Humidity Sensor In Fresh Air Intake Duct -G657-, REMOVING AND INSTALLING .
If the Air Quality Sensor -G238- function is OK during this test and there is a customer complaint, proceed as follows:
-- Check the dust and pollen filter for contamination. Refer to DUST AND POLLEN FILTER, REMOVING AND INSTALLING .
-- Select "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding " function.
A second technician is required to read out the displayed values while driving.
-- "Read the measured values" in turns for the Air Quality Sensor -G238- and the "recirculating/fresh air mode" request.
-- Drive the vehicle into an area with a relatively clean surrounding air.
- Specified value: System is working 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).
- Specified value: The information in the different display fields must change; for example, when driving through a diesel exhaust cloud.
Also observe the function descriptions for the Air Quality Sensor -G238- / and Humidity Sensor in Fresh Air Intake Duct -G657-. Refer to Air Quality Sensor -G238- FUNCTION .