Climate Control Exhaust Gas Sensor: Description and Operation

Air Quality Sensor (G238) Function

• The Air Quality Sensor is installed only on vehicles with a Comfort version A/C system.

• Air Quality Sensor detects pollutants in the ambient air (mostly gasoline and or diesel exhaust) and orders the Climatronic Control Module (J255) to switch the air conditioning system to recirculating air mode.

• Depending on setting in MMI (Multi Media Interface), the sunroof closes as soon as the Climatronic control module switches over to air recirculation mode (automatic air recirculation via the Air Quality Sensor or manual air recirculation by operating the air recirculation button). This function is equipment-dependent, its introduction has not yet been finalized. Refer to the Owner's Manual.

The Climatronic control module detects the type and intensity of air pollution at signal from sensor. Depending on the outside temperature and the intensity of air pollution, the Climatronic control module then decides:

- At an outside temperature greater than approximately: + 2 °C (36 °F) the recirculating air mode is switched on when there is only a slight increase in pollutants in the ambient air

- At an outside temperature between approximately + 2 °C (36 °F) and approximately - 8 °C (17.6 °F), the change over to recirculating air mode only occurs at a sharp increase of pollutant concentration, during which the compressor is switched on simultaneously

- At an outside temperature less than approximately - 8 °C (17.6 °F), the change over still occurs only at a sharp increase of pollutant concentration and then only for approximately 15 seconds (compressor is not switched on).

- If the pollution concentration in air drops, the climate control system switches over to the fresh air mode.

• The function Automatic air recirculation can be switched off at any time. If the function is active and a request for Automatic air recirculation is present the compressor is also switched on when outside temperatures are smaller than + 2 °C (36 °F). Compressor operation is not possible with temperatures lower than approximately - 8 °C (17.6 °F).

• At setting automatic air recirculation the Climatronic control module or in MMI (Multi Media Interface), compressor can be switched on also by switching on recirculating air manually (via recirculating air button) up to a temperature of approximately - 8 °C (17.6 °F).

• To ensure that the A/C does not operate constantly in the recirculating air mode in areas with a consistently higher pollution, the sensor is self-adapting (it adjusts its sensitivity to the environmental conditions).

• If outside air pollution load remains high for longer period of time, the sensor starts to adapt itself to the changing environmental condition through an adaptation program (learning program), the air recirculation request in evenly polluted ambient air is therefore generally shorter than 12 minutes. If a succession of peaks in the polluted air is detected, the air conditioning system can operate over a longer period of time in recirculated air mode.

• A certain amount of time is required for repositioning of the air conditioning system doors. In the event that a sudden increase in pollutants is encountered (for example, when driving through a diesel exhaust cloud) gaseous pollutants can be taken in with the fresh air into the passenger compartment until the doors can be closed. For this reason, a dust and pollen filter is installed with a charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced, refer to => [ Dust and Pollen Filter with Activated Charcoal Filter Unit ] Description and Operation.

• In order to avoid frequent shifting of the recirculating air/fresh air doors, a slight increase of pollutants in the ambient air will not allow for immediate shifting (the sensor does not send a request to the Climatronic control module). The filtering of the charcoal insert in the dust and pollen filter will be sufficient, refer to => [ Dust and Pollen Filter with Activated Charcoal Filter Unit ] Description and Operation.

• In order to avoid frequent shifting of the recirculated air/fresh air doors, the requirement from the Air Quality Sensor 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.

• If the compressor is shut-off (for example, in Econ mode), the maximum duration of the Automatic recirculating air mode is limited to approximately 15 seconds by the Climatronic control module to avoid windows from fogging up.

• So that fogged windows are cleared as quickly as possible, the Climatronic control module does not permit recirculating air operation during the Defrost operating mode.

• After the ignition is switched on, the Air Quality Sensor requires approximately 30 seconds to be operational (warm-up time). During this time there is no requirement from the Air Quality Sensor to the Climatronic control module for Automatic recirculating air mode.

• The Air Quality Sensor contains a highly sensitive electronic component which can be damaged if it comes in direct contact with solvents, fuels or chemicals. For this reason, do not install sensors that may have come into contact with these substances.