audi Workshop Repair Guides

Audi Workshop Service and Repair Manuals

ABOUT US
Checking air quality sensorG238 / humidity sender in fresh air intake duct G657 > < Coolant circulation pumpV50 (coolant pumpV36) on vehicles with a 6-cyl. petrol engine

A4 Mk3

Mode of operation of air quality sensorG238 and humidity sender in fresh air intake duct G657
Mode of operation of air quality sensor -G238- and humidity sender in fresh air intake duct -G657-
  Note
t  Different versions are fitted depending on the vehicle production period and the type of air conditioner („Basic“ or „Deluxe“). Until gradual conversion of the vehicle design as of Model Year 2012, air conditioners of the „Basic“ type were not fitted with a -G657- / -G238-. After this conversion, a -G657- with no -G238- (black housing) will be fitted. Until gradual conversion of the vehicle design as of Model Year 2012, the „Deluxe“ version was fitted with a -G238- with no -G657-. After this conversion, a -G657- with a -G238- (brown housing) will be fitted.
t  The air quality sensor -G238- without -G657- is only fitted on vehicles with an air conditioner of the „Deluxe“ type (as of start of production until conversion) → Electronic parts catalogue.
   
t  As of Model Year 2012, the design of the vehicles is being gradually converted, starting with the Audi A4 and Audi A5 → Chapter. On vehicles manufactured prior to conversion, air conditioners of the „Deluxe“ type are fitted with a -G238- (not fitted on „Basic“ version). On vehicles manufactured after this conversion (and on the Audi Q5 hybrid), the „Basic“ version is fitted with a -G657- and the „Deluxe“ version is fitted with a -G657- with -G238-.
t  The distinguishing features of the different versions are as follows: On the version with -G657- and -G238-, the housing is brown (gradual introduction as of model year 2012). On version -G657- with no -G238-, the housing is black (gradual introduction as of Model Year 2012). On version -G238- with no -G657-, the housing is black and there is no -G657--3- (gradual discontinuation as of Model Year 2012)
Mode of operation of air quality sensor -G238-:
t  There are different versions of the air quality sensor -G238--2-. This vehicle is fitted with an air quality sensor -G238- equipped with one sensor each for determining the NOx (nitrogen oxide) and CO (carbon monoxide) content of the air flowing past. The air quality sensor -G238- fitted on this vehicle also exchanges information with the onboard supply control unit -J519- via a local data bus. Attention must therefore be paid to the exact assignment of -G238- → Electronic parts catalogue.
t  The measured value of the air quality sensor -G238--1- is evaluated by the onboard supply control unit -J519- and transmitted via the data bus to the operating and display unit, Climatronic control unit -J255-. The operating and display unit, Climatronic control unit -J255- switches, on request, to air recirculation mode if there is no shut-off criterion → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  After switching on the ignition, the air quality sensor -G238- needs roughly 2 minutes to attain its operating temperature. The function of -G238- is restricted during the warm-up phase.
t  Under certain ambient conditions, an air quality sensor -G238- fault message may be displayed during the warm-up phase. Only replace -G238- if -G238- is permanently entered as being defective. If the fault display for -G238- changes from „static“ to „sporadic“ after switching the ignition off and on again (wait at least 2 minutes in each case), -G238- is OK and the event recorder entry requires no further attention (erase event recorder) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  The air quality sensor -G238- detects pollutants in the ambient atmosphere (generally petrol and/or diesel emissions) and causes the operating and display unit, Climatronic control unit -J255- to switch the air conditioner to air recirculation mode.
t  The operating and display unit, Climatronic control unit -J255- recognises the nature and level of the air pollution from the sensor signal. The decisions taken by the operating and display unit, Climatronic control unit -J255- are then governed by the ambient temperature and the severity of the air pollution → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  At ambient temperatures greater than approx. +2 °C, switching to air recirculation mode is implemented when requested by the air quality sensor -G238- as soon as there is a slight increase in pollutant concentration.
–  At ambient temperatures below approx. -1 °C and in „Econ mode“ (air conditioner compressor switched off, lamp in AC button not lit), switching only takes place if there is a considerable increase in pollutant concentration and only for approx. 15 s. If there is a renewed increase in pollutant concentration within approx. 2 minutes, the operating and display unit, Climatronic control unit -J255- does not switch to „automatic air recirculation mode“ within this period.
If the air conditioner compressor is switched off (e.g. in „Econ“ mode, lamp in AC button not lit), the maximum duration for „automatic air recirculation mode“ is restricted by the operating and display unit, Climatronic control unit -J255- to approx. 15 seconds to stop the windows misting up.
–  A decrease in concentration results in the air conditioner being switched back to fresh-air mode.
–  The duration of the „automatic air recirculation mode“ is governed by the type of operating and display unit, Climatronic control unit -J255-. At ambient temperatures below approx. +10 °C, the system remains in „automatic air recirculation mode“ for approx. 30 s for example. On completion of this period, the system is switched to fresh-air mode. In the event of a renewed increase in pollutant concentration within approx. 2 minutes, the operating and display unit, Climatronic control unit -J255- does not switch to „automatic air recirculation mode“ within this period.
t  The „Automatic air recirculation“ function can be deactivated at any time. If the function is active, the air conditioner compressor is switched on in the event of a request for „Automatic air recirculation mode“ even at ambient temperatures below +2 °C. At temperatures below approx. -5 °C compressor operation is however no longer possible again.
t  If „automatic air recirculation mode“ has been set in the MMI (Multi Media Interface), the air conditioner compressor may also be switched on with manually activated air recirculation (via the „air recirculation button“) down to temperatures of approx. -5 °C.
t  To prevent constant air conditioner air recirculation mode in areas with a persistently high level of pollutant emissions, the air quality sensor -G238- is adaptive (its sensitivity is matched to the environmental impact).
t  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 adaption program, with the result that an air recirculation 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 air recirculation mode for a longer period.
t  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 air flow/fresh-air flaps can close (and the air recirculation flaps open) in the event of a sudden increase in pollutant levels (e.g. on driving through a cloud of diesel emissions), vehicles with an air quality sensor -G238- are fitted 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 is to be replaced.
t  To stop the air flow/fresh-air flap and the air recirculation flap 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 (the air quality sensor -G238- does not transmit a request to the operating and display unit, Climatronic control unit -J255-). In such cases, the filter effect of the activated charcoal layer in the dust and pollen filter suffices.
t  To stop the air flow/fresh-air flap and the air recirculation flaps being switched too frequently, an air quality sensor -G238- request for „automatic air recirculation 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 air recirculation mode would no longer be necessary.
t  To clear misted windows as quickly as possible, the operating and display unit, Climatronic control unit -J255- does not permit air recirculation mode during „defrost“ operation (a request from the air quality sensor -G238- is not implemented).
t  The air quality sensor -G238- requires approx. 30 seconds to warm up after the ignition is switched on. During this period no request is sent by the air quality sensor -G238- to the operating and display unit, Climatronic control unit -J255- for „automatic air recirculation“.
t  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 fitted with sensors which have been in contact with such substances.
t  Certain ambient influences on switching on the ignition (e.g. a high pollutant content in the air) may result during the air quality sensor -G238- warm-up phase in a fault being stored for -G238- in the onboard supply control unit -J519- although the sensor is OK. The following action is then to be taken:
–  Switch off the ignition for at least 2 minutes.
–  Switch on the ignition and wait at least 2 minutes.
–  Read out the event recorder of the onboard supply control unit -J519-. If a static fault is still displayed for the air quality sensor -G238-, perform guided fault-finding → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. If a fault is no longer displayed for the air quality sensor -G238- or if the fault is now sporadic, the air quality sensor -G238- is OK (and further observation is not necessary). Erase the event recorder.
  A87-10906
Mode of operation of humidity sender in fresh air intake duct -G657-:
t  With the version for vehicles with an air conditioner of the „Deluxe“ type, the -G657--Item 3- is accommodated together with -G238--Item 1- in a joint housing -2- (housing colour „brown“).
t  With the version for vehicles with an air conditioner of the „Basic“ type, only -G657--Item 3- is fitted. There is no -G238--Item 1- in the housing -2- (housing colour „black“).
t  -G657- is a highly sensitive electronic component which could be destroyed by direct exposure to fluids, solvents, fuels and certain chemical compounds.
t  In addition, direct contact with water can impair operation of -G657- to such an extent that correct humidity measured values can no longer be determined (either briefly or permanently depending on the composition of the fluid). The vehicle should therefore not be fitted with sensors which have been in contact with such substances.
t  -G657- determines the temperature and the moisture content of the air flowing past and exchanges information with the onboard supply control unit -J519- by way of the data bus.
t  The measured value of -G657- is evaluated by -J519- and transmitted to the operating unit, Climatronic control unit -J255- via the data bus.
t  -J255- uses the measured values to calculate the current relative humidity of the fresh air drawn in. The calculated humidity value then indicates whether there is a risk of the windscreen, rear window and door windows misting up from the inside. If this is the case, -J255- takes corrective action by altering various characteristic curves. This may involve a reduction in evaporator temperature (by way of air conditioner compressor actuation), an increase in the response thresholds for the request for „Automatic air recirculation mode“ or prevention of engine shut-off via the start-stop function for example.
t  After switching on the ignition, -G657- needs roughly 2 minutes to attain its operating temperature. The function of -G657- is restricted during the warm-up phase.
  A87-10906

Checking air quality sensorG238 / humidity sender in fresh air intake duct G657 > < Coolant circulation pumpV50 (coolant pumpV36) on vehicles with a 6-cyl. petrol engine