Climate Control Exhaust Gas Sensor: Description and Operation
Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657)
Depending on the equipment, the air quality sensor is available individually or together with the humidity sensor in fresh air intake duct in one shared housing. Allocation, refer to Electronic Parts Catalog (ETKA).
• In the Basic version of the A/C system, only the humidity sensor in fresh air intake duct is installed.
• In the Comfort version of the A/C system, an air quality sensor is integrated in the housing in addition to the humidity sensor in fresh air intake duct.
Mode of Operation Of Air Quality Sensor (G238)
• The air quality sensor - 2 - uses a sensor to determine the NOx level (nitrogen oxide) and the CO level (carbon monoxide) in the air flowing past, and exchanges this information with the Vehicle electrical system control module (J519) via the data bus.
• The measured value of the air quality sensor is evaluated by the Vehicle electrical system control module and is transmitted via the data bus to the Climatronic control module (J255). Upon request, the Climatronic control module switches to recirculation mode if no shut-off condition is present. Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• Certain A/C system functions (for example, control of the "automatic recirculation mode") can be switched on and off via the MMI (Multi Media Interface) in the "A/C system" function in the "Car"/"Car systems" menu.
• The air quality sensor needs about 2 minutes to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the air quality sensor is limited.
• The air quality sensor detects pollutants in the ambient air (usually gasoline and/or diesel exhaust) and causes the Climatronic control module to switch the A/C system to recirculation mode.
• The Climatronic control module, recognizes the type and intensity of the air pollutant on the basis of the signal from the air quality sensor (Comfort version). Moreover, the Climatronic control module receives the sensitivity set by the Multimedia system control head (E380) via the data bus. Based on this information, the Climatronic control module then decides whether and when the A/C system is switched to recirculation mode.
Example:
- At an outside temperature above approximately +2° C (35° F), the recirculation mode is switched on upon request from the air quality sensor when there is only a slight increase in the pollutants in the ambient air.
- In the case of an outside temperature of less than approximately -1° C (30° F) and if the A/C compressor is switched off, the switch is first made in the case of a significant increase in the pollution concentration and only for approximately 15 seconds. If another increase in the pollutant concentration occurs within approximately 2 minutes, the Climatronic control module does not switch within this time to "automatic recirculation mode".
• The warning light in the AC button does not illuminate.
• The maximum duration of the "automatic recirculation mode" is limited by the Climatronic control module to approximately 15 seconds - so that the windows of the passenger compartment do not fog up.
- If the concentration decreases, the air conditioner switches to the fresh air mode.
• The duration of "automatic recirculation mode" depends on the version of the Climatronic control module and the setting on the Multimedia system control head.
- If the outside air temperature is below approximately +10° C (50° F)and the Multimedia system control head is set to maximum sensitivity, the system will stay on for approximately 30 seconds in "automatic recirculation mode". After this, it switches back to fresh air mode. If another increase in the pollutant concentration occurs within approximately 2 minutes, the Climatronic control module does not switch to "automatic recirculation mode" during this time.
• The "automatic recirculation mode" function can be switched off at any time. If the function is active, the A/C compressor is switched on with a request for "automatic recirculation mode" and also when the outside air temperature is below +2° C (35° F). If the temperature is below -5° C (23° F), then the A/C compressor will not turn on.
• In the case of the "automatic recirculation mode" setting in the MMI (Multi Media Interface), the A/C compressor can be switched on to a temperature of approximately -5° C (23° F).
• To ensure that the A/C system does not operate constantly in recirculation mode in areas with a consistently high pollution, the air quality sensor is self-adapting (it adjusts its sensitivity to the environmental conditions).
• If the outside air pollution load remains relatively high for a long period of time, the air quality sensor starts to adapt itself to the changing environmental conditions through an adaptation program (learning program) so that 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 airflow doors/fresh air doors can be closed. For this reason, a dust and pollen filter is installed with an activated charcoal layer. A filter that is saturated with pollutants is no longer effective and needs to be replaced.
• To prevent excessive operation of the back pressure/fresh air door and the air recirculation door, the door is not actuated immediately if there is a nominal increase in pollutants in the outside air (the air quality 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.
• In order to avoid excessive operation of the back pressure/fresh air door and the air recirculation door, a request from the air quality sensor for "automatic recirculation mode" remains active for at least 25 seconds (minimum duration period), even if the pollutant concentration is so far reduced that recirculation mode is no longer necessary.
• To defog fogged-up windshield, rear window, and door windows as quickly as possible, the Climatronic control module does not allow recirculation mode in the "defrost" mode (a request from the air quality sensor is not implemented).
• The Air quality sensor (G238) requires approximately 2 minutes to be ready for operation after the ignition is switched on (warm-up time). No request for "automatic recirculation mode" is sent to the Climatronic control module.
• Under certain ambient influences, when switching on the ignition (for example, when the air pollution is high), if a fault on the air quality sensor is stored in the Vehicle electrical system control module during the air quality sensor warm-up time, even though the sensor is OK, proceed as follows:
- Switch off the ignition for minimum 2 minutes.
- Switch on the ignition and wait at least 2 minutes.
- Read the event memory of the Vehicle electrical system control module. If the air quality sensor still displays a static malfunction, perform Guided Fault Finding using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. If the air quality sensor is no longer displayed as a malfunction, or the malfunction is sporadic, the air quality sensor is OK (and does not need to be observed). Erase the event memory.
Mode Of Operation Of The Humidity Sensor In Fresh Air Intake Duct (G657)
The Humidity Sensor In Fresh Air Intake Duct - 3 - is situated with the Air Quality sensor - 1 - in a shared housing - 2 -.
• The humidity sensor in fresh air intake duct is a highly sensitive electronic component which can be damaged if it comes in direct contact with liquids, solvents, fuels or certain chemical compounds.
• Moreover, the function of the humidity sensor in fresh air intake duct can be severely affected by direct contact with water so that correct moisture values can no longer be measured (briefly or permanently depending on the composition of the fluid). For this reason, do not install sensors that may have come into contact with these substances.
• The humidity sensor in fresh air intake duct determines the temperature and the moisture in the air flowing past and exchanges the information with the Vehicle electrical system control module via the data bus.
• The measured value of the humidity sensor in fresh air intake duct is evaluated by the Vehicle electrical system control module and is transmitted via the data bus to the Climatronic control module.
• Certain A/C system functions (for example, control of the "automatic recirculation mode") can be switched on and off via the MMI (Multi Media Interface) in 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.
• The Climatronic control module uses the measured values to calculate the current relative humidity of the drawn-in fresh air. The calculated humidity value is used to detect whether there is a risk of the windshield, rear window, and door windows fogging up on the inside. If that is the case, the Climatronic control module changes various characteristic curves to counteract this. This can be performed, for example, by lowering the evaporator temperature (by activating the A/C compressor), by raising the response thresholds for the request for "automatic recirculation mode", by preventing engine shut-off via the start-stop function, etc.
• The humidity sensor in fresh air intake duct needs about 2 minutes to reach its operating temperature after the ignition is switched on. During the warm-up phase, the function of the humidity sensor in fresh air intake duct is limited.