Air Quality Sensor G238
Air Quality Sensor G238
- The Instrument Cluster Control Module detects pollutants in the ambient atmosphere (generally gasoline emissions) and causes the operating and display module, Climatronic Control Module J255 to switch the air conditioner to "recirculated-air mode".
- The operating and display module, Climatronic Control Module J255 recognizes the nature and level of the air pollution from the Air Quality Sensor G238 signal. Depending on ambient temperature and the degree of air pollution, the operating and display module, Climatronic Control Module J255 effects the following:
- At ambient temperatures greater than approx. - 2 degrees C, even a slight increase in pollutant concentration causes switching to recirculated-air mode.
- At ambient temperatures between approx. - 2 degrees C and approx. -8 degrees C, switching to recirculated-air mode and simultaneous cut-in of compressor only take place in the event of a considerable increase in pollutant concentration.
- At ambient temperatures below approx. -8 degrees C, switching likewise only takes place in the event of a considerable increase in pollutant concentration and the time period is restricted to approx. 15 s (compressor does not switch on).
- A decrease in concentration results in the air conditioner being switched back to "fresh-air mode".
- The "automatic air recirculation" function can be deactivated at any time. If the function is active, the compressor is switched on in the event of a request for "automatic air recirculation" even at ambient temperatures below - 2 degrees C. At temperatures below approx. - 8 degrees C compressor operation is however also no longer possible.
- On vehicles with "automatic air recirculation", the compressor may also be switched on with manually activated air recirculation (via "recirculated-air button") down to temperatures of approx. - 8 degrees C.
- To prevent constant air conditioner recirculated-air mode in areas with a persistently high level of pollutant emissions, the Air Quality Sensor G238 is adaptive (sensitivity is matched to environmental impact).
- If the pollutant level in the ambient air remains relatively high for a lengthy period, the Air Quality Sensor G238 starts to adapt to the change in ambient conditions by way of an adaptation program, with the result that a recirculated-air request is generally applied for less than 12 minutes given uniform ambient air pollution. In the event of several consecutive peak impact levels, the air conditioner may also operate in recirculated-air mode for a longer period.
- Switching of the air conditioner flaps takes a certain length of time. To prevent gaseous pollutants entering the passenger compartment together with the fresh air drawn in before the fresh-air flaps can close in the event of a sudden increase in pollutant levels (e.g. on driving through a cloud of diesel emissions), the vehicle is installed with a dust and pollen filter provided with an activated charcoal layer. Once a filter is saturated with pollutants, it can no longer perform this function and must be replaced.
- To stop the "recirculated-air/fresh-air flaps" being switched too frequently, switching does not take place immediately in the event of a slight increase in the pollutant level in the ambient atmosphere ( Air Quality Sensor G238 does not transmit request to operating and display module, Climatronic Control Module J255 ). In such cases, the filter effect of the activated charcoal layer in the dust and pollen filter suffices.
- To stop the "recirculated-air/fresh-air flaps" being switched too frequently, an Air Quality Sensor G238 request for "automatic recirculated-air mode" is applied for at least 25 s (minimum dwell time) even if the pollutant concentration in the air has decreased again to such an extent that recirculated-air mode would no longer be necessary.
- If the compressor is switched off (e.g. in "Econ" mode), the maximum duration for "automatic recirculated-air mode" is restricted by the operating and display module, Climatronic Control Module J255 to approx. 15 seconds to stop the windows misting up.
- To clear misted windows as quickly as possible, the operating and display module, Climatronic Control Module J255 does not permit recirculated-air mode during "defrost" operation.
- The Air Quality Sensor G238 requires approx. 30 seconds to warm up after ignition is switched on. During this period No request is sent by the Air Quality Sensor G238 to the operating and display module, Climatronic Control Module J255 for "automatic air recirculation".
- The Air Quality Sensor G238 is a highly sensitive electronic component which could be destroyed by direct exposure to solvents, fuels and certain chemical compounds. The vehicle should therefore not be installed with Air Quality Sensor G238 which have been in contact with such substances.
Air Quality Sensor G238 , Checking
Special tools and equipment
- Diagnostic Operation System VAS 5051A e.g. with Diagnostic Cable - 3 Meter VAS 5051/5A and K-Lead Adapter Vas6017B VAS 6017B (or K-Lead Adapter VAS 6017A )
- Test gas "D 007 855 A2"
NOTE:
- The vehicle must be standing in a clean atmosphere (away from running engines, exhaust vents, etc.).
- The engine compartment and plenum chamber must be clean (not contaminated with oil or fuel).
- The engine compartment and plenum chamber must not have been sprayed with cleaning agents or preservatives containing solvents.
Checking
- Remove plenum chamber cover.
- With the ignition switched off, connect Diagnostic Operation System VAS 5051A using, for example, Diagnostic Cable - 3 Meter VAS 5051/5Aand K-Lead Adapter Vas6017B VAS 6017B (or K-Lead Adapter VAS 6017A) to the 16-pin diagnostic socket in the vehicle. Diagnostic Operation System VAS 5051A, Connecting and Selecting Functions
- Start engine.
- Check DTC memory Displaying & Reading Trouble Codes
- On operating and display module, Climatronic Control Module J255 , set "Auto" mode.
- "Automatic air recirculation" button - A - pressed (LED in button - A - lights).
- Wait 30 s to allow Air Quality Sensor G238 to warm up.
Indicated on display of Diagnostic Operation System VAS 5051A:
- Select function "08 - Reading measuring value block".
Indicated on display of Diagnostic Operation System VAS 5051A
- Prompt for entering display group appears in display zone -1 -. -
- Input keypad appears in display zone - 2 -.
- Use input keypad in display zone - 2 - to enter desired display group number "014". Measuring Value Blocks (Function 08)
- Confirm entry with Q key.
- Read displays in zones "3" and "4".
NOTE: Display field "4" indicates operating status of air conditioner (fresh-air or recirculated-air mode), whereas display zone "3" shows status of Air Quality Sensor G238 signal. Remarks on possible displays and
Specified value in display zone "4"
- "00" (no request for "recirculated-air mode" , air conditioner in fresh-air mode)
Or
- "60" ("partial recirculated-air mode", fresh-air and recirculated-air flap open)
- Position spray attachment - A - of test gas canister over air inlet of Air Quality Sensor G238 - B - (with version "1" of Air Quality Sensor G238 ).
- Position spray attachment - A - of test gas canister over air inlet of Air Quality Sensor G238 - B - (with version "2" of Air Quality Sensor G238 ).
- Press spray knob - C - of test gas canister for approx. 1 second.
NOTE:
- There are different Air Quality Sensor G238 housings. Version "1" was installed at the start of production. This sensor is gradually being replaced by version "2", however the mode of operation is identical.
- The test gas canister is filled with pure oxygen with a specific nitrogen oxide component.
- The Air Quality Sensor G238 also reacts when exposed to cigarette smoke or cigarette lighter gas (gas is heavier than air, the Air Quality Sensor G238 must therefore be removed and turned round).
- Read off display in zone "4".
Specified value:
- "10" ("Automatic air recirculation mode" requested, request met, air conditioner switches to recirculated-air mode)
- Wait briefly approx. 1 minute, depending on amount of test gas sprayed onto Air Quality Sensor G238).
- Read off display in zone "4".
Specified value:
- "00" (no request for "recirculated-air mode" , air conditioner in fresh-air mode)
Or
- "60" (Partial recirculated-air mode)
NOTE: To stop the recirculated-air/fresh-air flaps being switched too frequently, an Air Quality Sensor G238 request for "automatic recirculated-air mode" is applied for at least 25 s (minimum dwell time) even if the pollutant concentration in the air has decreased to such an extent that recirculated-air mode would no longer be necessary.
- Activate windshield wash/wipe switch until Windshield Washer Pump V5 has conveyed fluid for approx. 2 s.
- Read off display in zone "4".
Specified value:
- "30" ("Recirculated-air mode" requested because of windshield washer system, air conditioner switches to recirculated-air mode for approx. 10 sec.)
NOTE: The request for "recirculated-air mode" during windshield washer system operation is not implemented with all versions of the operating and display module, Climatronic Control Module J255.
- Wait briefly.
- Read off display in zone "4".
Specified value:
- "00" (no request for "recirculated-air mode" , air conditioner in fresh-air mode)
Or
- "60" (Partial recirculated-air mode)
NOTE:
- Depending on the composition of the windshield washer fluid, the Air Quality Sensor G238 may detect air pollution and request "Automatic air recirculation".
- If switching to recirculated-air mode does not take place on activating windshield wipe/wash switch, check operation of Wiper/Washer Intermittent Relay J31 if applicable ("windshield wash" information is received via the CAN-Bus comfort system from the Steering Column Electronic Systems Control Module J527 ) (Reading measuring value block, display group "018").
Proceed as follows if the Air Quality Sensor G238 functions properly in this test but a customer complaint has been received:
- Check for contamination of dust and pollen filter.
- Connect Diagnostic Operation System VAS 5051A for example and select function "08 Reading measuring value block" for air conditioner.
- Enter display group number "014" and read off displays in zones "3" and "4".
NOTE:
- A second person is required to read out the values displayed while driving.
- Pay attention to safety precautions.
- Perform a test drive, starting in an area with a relatively clean ambient atmosphere (system operating in fresh-air mode) and then proceeding to an area where the atmosphere is polluted (e.g. uphill road with truck traffic).
NOTE:
- The display in zones "3" and "4" in display group "014" must change, for example, on driving through a cloud of diesel emissions. Measuring Value Blocks (Function 08)
- Also pay attention to the notes on the dust and pollen filter and on operation of the Air Quality Sensor G238.