Climate Control Exhaust Gas Sensor: Description and Operation
Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) Function
• There are different versions depending on the vehicle date of manufacture and which A/C system ("Basis" or "Comfort") is installed. The "Basis" A/C system does not have a humidity sensor in fresh air intake duct / air quality sensor until the MY 12 change-over. From MY 12 it has a humidity sensor in fresh air intake duct without an air quality sensor (black housing). Through MY 12, the "Comfort" A/C system has an air quality sensor without a humidity sensor in fresh air intake duct. From MY 12, it has a humidity sensor in fresh air intake duct with an air quality sensor, (brown housing).
• Only vehicles with the "Comfort" A/C system have an without a humidity sensor in fresh air intake duct (from start of production up the change-over) Refer to the Electronic Parts Catalog.
• Beginning with the MY 12 Audi A4 and Audi A5, the vehicle version was changed-over as a running change. Refer to => [ Climatronic Control Module (J255) A/C Control Head Allocation ] Climatronic Control Module (J255) A/C Control Head Allocation. Vehicles, built before the change-over and with the "Comfort" A/C system, have an air quality sensor (not on the "Basis"). Vehicles built since this change-over (and on the Audi Q5 Hybrid): if the vehicle has the "Basis" A/C system, then it has a humidity sensor in fresh air intake duct; if the vehicle has the "Comfort" A/C system, then it has a humidity sensor in fresh air intake duct and an air quality sensor.
• This is how to tell the difference: the humidity sensor in fresh air intake duct with an air quality sensor has a brown housing (running change from MY 12). The humidity sensor in fresh air intake duct with an air quality sensor has a black housing (running change from MY 12). The air quality sensor without the humidity sensor in fresh air intake duct has a black housing and the humidity sensor is fresh air intake duct - 3 - is not there (discontinued as a running change from MY 12).
Air Quality Sensor Function (G238) :
• There are different versions of the air quality sensor - 2 -. This vehicle has an air quality sensor that determines the NOx portion (nitrogen) and CO portion (carbon monoxide) of the air flowing by via a sensor. In addition, the air quality sensor exchanges information with the vehicle electrical system control module (J519) via a local Data bus. Note the exact allocation, refer to the air quality sensor in the Electronic Parts Catalog.
• The vehicle electrical system control module (J519) measures the value from the air quality sensor - 1 - and transmits it to the Climatronic control module (J255) via the Data bus. The Climatronic control module switches to recirculating air mode when requested, if there are no shut-off conditions present using the Vehicle Diagnostic Tester under "Guided Fault Finding".
• 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.
• During the warm-up phase, air quality sensor malfunctions may occur under certain ambient conditions. Replace the air quality sensor only if it is registered continually as faulty. If the malfunction display for the air quality sensor changes from "static" to "sporadic" after turning off the ignition, waiting 2 minutes and then turning it back on, then the air quality sensor is OK and it is no longer necessary to observe the DTC memory. Refer to the Vehicle Diagnostic Tester in "Guided Fault Finding".
• The air quality sensor recognizes the pollutants in the surrounding air (mostly gasoline and/or diesel exhaust gases) and switches the Climatronic control module to recirculating air mode.
• The Climatronic control module recognizes the type and intensity of the air pollutant on the signal from the sensor. The Climatronic control module display and control head then makes the decision based on the outside air temperature and the intensity of the air pollutant. Check using the Vehicle Diagnostic Tester under "Guided Fault Finding".
- If there is already a slight increase in the pollutant concentration in the air, the air quality sensor requests to switch on the recirculating air mode when the outside air temperature goes above +2 °C (35°F).
- If the outside air temperature goes below -1 °C (30 °F) and in "ECON mode" (the A/C compressor is switched off and the indicator lamp in the button is off) the switch-over takes place first when there is a sharp increase in the pollutant concentration and only for 15 seconds. If there is another increase in the pollutant concentration within another 2 minutes, then the Climatronic control module does not switch into the "recirculating air mode".
If the A/C compressor is off (for example, "ECON" is on and the indicator lamp in the AC button is off), the Climatronic control module) A/C control head will limit the time the "recirculating air mode" is on to 15 seconds (so that the windows do not fog up).
- If the concentration decreases, the air conditioner switches to the fresh air mode.
- The duration of the "automatic recirculating air mode" depends on the version of the Climatronic control module display and control head. If the outside air temperature is below +10 °C (50 °F), then the system will stay on for approximately 30 seconds in "automatic recirculating air". After this, it switches back to fresh air mode. If, within 2 minutes, an increase in the pollutant concentration occurs, the Climatronic control module does not switch over to "automatic recirculating air mode" during this time.
• "Automatic recirculating air mode" can be switched off at any time. If the function is active, the A/C compressor is switched on with a request for "automatic recirculating air mode" and also when the outside air temperature is below +2 °C (35 °F). If the temperature is below -5 °C (23 °F), then it is not possible to use the A/C compressor.
• If "automatic recirculating air mode" is selected in MMI (Multi Media Interface), then the A/C compressor can be switched on by manually switching on recirculating air mode (using the "air recirculation button") down to -5 °C (23 °F).
• To ensure that the A/C does not operate constantly in the recirculating air mode in areas with a consistently higher pollution, the Air Quality Sensor is self learning (it adjusts its sensitivity to the environmental conditions).
• If outside air pollution load remains high for longer period of time, the Air Quality 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 door can be closed. For this reason, on vehicles equipped with a Air Quality Sensor 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.
• In order to avoid frequent shifting of the fresh /recirculating air doors, a slight increase of pollutants in the ambient air will not allow for immediate shifting (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 frequent shifting of the recirculated air/fresh air doors and the recirculation 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.
• So that fogged windows are cleared as quickly as possible, Climatronic control module does not allow air recirculation when "Defrost" is on (a request from the Air Quality Sensor is not processed).
• After the ignition is switched on, air quality sensor requires approximately 30 seconds to be operational (warm-up time). During this time there is no request from the air quality sensor to the Climatronic control module display and control head 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.
• 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 (J519) 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 minimum 2 minutes
- Read the DTC memory for the vehicle electrical system control module (J519). 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, then the air quality sensor is OK and does no longs needs to be observed. Erase the DTC memory.
Humidity sensor in fresh air intake duct function button (G657) :
• The humidity sensor in fresh air intake duct - 3 - and the air quality sensor - 1 - are installed in the same housing - 2 - (housing color "brown") on vehicles with the "Comfort" A/C system.
• If the vehicle has the "Basis" A/C system, then only the humidity sensor in fresh air intake duct - 3 - is there. The air quality sensor - 1 - is not installed in the housing - 2 - (housing color "black").
• The humidity sensor in the fresh air intake duct is a highly sensitive electronic component that can be damaged if it comes in direct contact with fluids, solvents, fuels and certain chemical compounds.
• The function of the humidity sensor in the 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 the fresh air intake duct determines the temperature and the moisture in the flowing air and exchanges the information with the vehicle electrical system control module (J519) via the Data bus.
• The measured value for the humidity sensor in the fresh air intake duct is taken from the vehicle electrical system control module and transferred via the Data bus to the Climatronic control module (J255) control head.
• 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 Climatic 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 motor shut-off via the start-stop function, etc.
• The humidity sensor in the 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 the fresh air intake duct is limited.