Air Quality Sensor -G238-, Checking
The Air Quality Sensor -G238- -A- requires about two minutes after the ignition has been switched on before it reaches its operational temperature.
During the warm-up phase, function is limited and malfunctions may occur under certain ambient conditions. If the malfunction display for the Air Quality Sensor -G238- changes after switching the ignition off and back on again (wait at least two minutes) from "static" to "sporadic", the Air Quality Sensor -G238- is OK and it is no longer necessary to pay attention to the DTC memory entry (erase the event 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" / "car systems" menu. The A/C system control can also be influenced via presettings in the MMI (Multi Media Interface) under the "A/C system" function in the "car" / "car systems" menu. Therefore, first check the presetting in the MMI in the case of a problem with these components, refer to Infotainment/MMI Operating Instructions.
Special tools and workshop equipment required
- Vehicle Diagnostic Tester
- Commercial gas lighter
Test Requirements
-- The vehicle is standing in a clean atmosphere.
- Away from running engines, exhaust vents, etc.
-- The 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" / "car systems" menu in the MMI (Multi Media Interface), refer to Infotainment/MMI operating instructions.
Functionality, Checking
-- Remove the Air Quality Sensor -G238-. The connector remains connected, refer to Air Quality Sensor -G238- WITH Humidity Sensor In Fresh Air Intake Duct -G657-, REMOVING AND INSTALLING .
-- Start the engine.
-- Set the "Auto" mode on the Climatronic Control Module -J255-.
-- Set "automatic recirculation mode" via the MMI (Multi Media Interface) in the Climatronic Control Module -J255-, refer to Infotainment/MMI Operating Instructions.
- The Air Quality Sensor -G238- is operational after two minutes warm-up time.
-- Check the Diagnostic Trouble Code (DTC) memory for the Climatronic Control Module -J255- control head and select "Read measured values", refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
-- Read the measured values for the Air Quality Sensor -G238-. The air pollution measured by the Air Quality Sensor -G238- is displayed.
- The value for the NOx level (nitrogen oxide) and CO level (carbon monoxide) in the air.
- For an explanation of the possible displays, refer to the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
-- Allow a little bit of gas from the lighter -B- to flow past from the top area -A- of the Air Quality Sensor -G238-.
If the Air Quality Sensor -G238- comes in contact with gas from a lighter, it will react. Gas from a lighter is heavier than air, therefore remove the Air Quality Sensor -G238- to avoid contamination from above.
-- Read the measured values for the Air Quality Sensor -G238-.
- Specified value: In the display fields, the measured values for the "CO level" change with respect to the initial value, thus indicating that the "CO level" sensor in the Air Quality Sensor -G238- is functioning properly and the Air Quality Sensor -G238- electronics are evaluating the measured values correctly.
The "NOx level" sensor currently cannot be tested with shop equipment. However, if the air composition around the sensor changes, the displayed value for the "NOx level" also changes.
-- Wait a short period of time (approximately one minute, depending on amount of test gas flowing into the sensor).
-- Read the measured values for the Air Quality Sensor -G238-.
- Specified value: The measured values will return to the output values and by doing so, show that both sensors are working correctly, and that the sensor electronics evaluated 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 display with the measured values for the A/C operating status (recirculation/fresh air operation).
- Target value: The display field will show that the A/C is working in the fresh air mode.
If the "Read the Measured Values for Display Group" function displays a different "Fresh Air Mode" value, there is a request for circulating air mode (for example due to the request for "maximum cooling output" or the "manual recirculation mode" setting). Select an operating mode, which does not require recirculated air mode.
If it is shown in the "Read measured values" function that the Air Quality Sensor -G238- is already requesting "automatic recirculation mode", clean the plenum chamber if necessary or move the vehicle into an area where the air is cleaner.
-- Allow a little bit of gas from the lighter -B- to flow past from the top area -A- of the Air Quality Sensor -G238-.
-- Read the measured values for the Air Quality Sensor -G238-.
-- Read the recirculation/fresh air mode display.
- Target values: There is a request for the recirculating air mode and the A/C system is operating in recirculating air mode.
If it is shown in the "read measured values" function that the Air Quality Sensor -G238- is requesting "automatic recirculation mode", but the request cannot be implemented due to a shut-off condition from the Climatronic Control Module -J255- control head, eliminate the cause of this shut-off condition if necessary.
In order to avoid frequent shifting of the recirculated air/fresh air doors and the recirculation doors, the requirement of the Air Quality Sensor -G238- for "Automatic air recirculation" mode remains for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that recirculated air mode is no longer necessary.
-- Wait a short period of time (approximately one minute, depending on amount of test gas flowing into the sensor).
- Target value: There is no longer a request for recirculating air mode, and the A/C system is working again in the fresh air mode.
-- Install the Air Quality Sensor -G238-, refer to Air Quality Sensor -G238- WITH Humidity Sensor In Fresh Air Intake Duct -G657-, REMOVING AND INSTALLING .
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 Dust And Pollen Filter, Removing And Installing .
-- Select "Read measured values" using the => in the "Guided Fault Finding" function.
A second person is required to read out values displayed while driving.
Observe the safety precautions, refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" Function.
-- Read the displays in the "Read measured values" function for the Air Quality Sensor -G238- measured values and the recirculation/fresh air mode request.
-- Drive the vehicle into an area with a relatively clean atmosphere.
- Target value: System operates in fresh-air mode.
-- Then drive vehicle into an area where the atmosphere is polluted (for example, onto an uphill road with truck traffic).
- Specified value: The displays 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- AND Humidity Sensor in Fresh Air intake Duct -G657-, FUNCTION .