Air Quality Sensor -G238-, Checking
Special tools and workshop equipment required
- Vehicle Diagnostic Tester
- Commercial gas lighter
The Air Quality Sensor -G238- -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 (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, check the preset in the MMI first in case there is a concern regarding these components. Refer to Infotainment/MMI Operating 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.
It is possible to switch the "automatic recirculating air mode" on or off via the "A/C" function in the "car" / "car systems" menu in the MMI (Multi Media Interface). Refer to the Infotainment/MMI operating instructions.
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.
-- Set the "Auto" mode on the Climatronic Control Module -J255-.
-- Set "automatic recirculating air mode" via the MMI (Multi Media Interface) in the Climatronic Control Module -J255-. Refer to the Infotainment/MMI Operating Instructions.
- The Air Quality Sensor -G238- is operational after approximately two minutes warm-up time.
-- Check the DTC memory for the Climatronic Control Module -J255- control head and select "Read measured values". Use 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 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.
- 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.
- Specified value: 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.
- Specified value: The display field shows that the A/C system is working in 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).
-- "Read the measured values" for the fresh air and recirculating air mode status (depending on the measured value of the Air Quality Sensor -G238-).
- Specified value: if the measured values go back to the initial values in the display fields, this indicates that the sensors in the Air Quality Sensor -G238- are working correctly and the electronics of the Air Quality Sensor -G238- are evaluating the measured values correctly. Use 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 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.
-- 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 .