Sensor for air quality -G238-, checking: Checking

Switch ignition on.
Set A/C control head -E87- to "Auto" operating mode.
Start engine (compressor on).
Press button for "Automatic air recirculation" (lamp in -A- button comes on).

Fig 1: Locating Automatic Air Recirculation Button

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Wait 30 seconds (warm-up time of sensor for air quality -G238-).
Connect VAG 1551 Scan Tool (ST) to 16-pin Data Link Connector (DLC) using VAG 1551/3 adapter cable. See VAG 1551 (VAG 1552) SCAN TOOL (ST), CONNECTING AND SELECTING FUNCTIONS .

Fig 2: Connecting Scan Tool To Data Link Connector

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Start engine.
The on board diagnostic function for A/C control head -E87- begins (address word "08"). See READ MEASURING VALUE BLOCK (FUNCTION 08) .

Indicated on display

Fig 3: Scan Tool Display - Select Function xx
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Press buttons -0- and -8- to select "Read Measuring Value Block" function 08.
Indicated on display

Fig 4: Scan Tool Display - 08, Read Measuring Value Block

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Press -Q- button to confirm input.
Indicated on display

Fig 5: Scan Tool Display - Input Display Group Number XXX

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Input display group number "01" (overview. See READ MEASURING VALUE BLOCK (FUNCTION 08) ).
Press -Q- button to confirm input.
Indicated on display

Fig 6: Scan Tool Display - Read Measuring Value Block 1

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Display "0" in display field 1 shows the compressor switched on (there is no compressor cut-off condition).

Fig 7: Scan Tool Display - Display Field 2, A/C Clutch Voltage (12.5 V)
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Table of possible displays in display field 1. See DISPLAY GROUP 001 - A/C COMPRESSOR CUT-OFF CONDITIONS, VOLTAGE FOR A/C CLUTCH -N25-, VOLTAGE TO TERMINAL 15 AND REQUIREMENT FOR RECIRCULATING AIR MODE/SENSOR FOR AIR QUALITY -G238- .
The voltage for the A/C clutch -N25- is displayed in display field 2 (for example, 12.5 V).
Display field 3 shows the voltage to terminal 15 (for example, 12.5 V).
Display field 4 shows operating condition of the fresh/recirculating air. Table of possible displays in display field 4. See DISPLAY GROUP 001 - A/C COMPRESSOR CUT-OFF CONDITIONS, VOLTAGE FOR A/C CLUTCH -N25-, VOLTAGE TO TERMINAL 15 AND REQUIREMENT FOR RECIRCULATING AIR MODE/SENSOR FOR AIR QUALITY -G238- .

Read display from display field 4.

Fig 8: Scan Tool Display -Display Field 4
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Specified values: "00" (no requirement for "recirculating air", A/C in fresh air mode with fresh air operation) or "60" ("Partial recirculating air," fresh air and recirculating air flap open)
Place spray head -A- of test bottle over air inlet of sensor for air quality -B-.
Activate spray head -C- of test bottle for 1 second.

Fig 9: Placing Spray Head Of Test Bottle Over Air Inlet Of Sensor For Air Quality
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NOTE:

The content of the test gas bottle consists of pure oxygen with a specified amount of nitrogen oxide.
The test gas for the air quality sensor is obtained as a replacement part under the number D007 855 A2.
If the sensor comes in contact with cigarette smoke or gas from a lighter it will react.

CAUTION: Part numbers are listed here for reference only. Always check with your Parts department for the latest information.

Read display from display field 4.
Specified value: "10" (requirement for "Automatic air recirculation" available, requirement is fulfilled, A/C switches to recirculating air mode)

Fig 10: Scan Tool Display -Display Field 4, Specified Value 10

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Wait a short period of time (approx. 1 minute, depending on amount of test gas sprayed in sensor).
Read display field 4.
Specified value: "00" (no requirement for "Recirculating air," A/C system in fresh air mode or "60" (partial recirculating air)

Fig 11: Scan Tool Display -Display Field 4, Specified Value 00

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NOTE: In order to avoid quick shifting from the recirculating air/fresh air flap, the requirement from the sensor for "Automatic air recirculation mode" is at least 25 seconds (minimum duration period) especially if the pollutant concentration has been reduced considerably so that recirculating air mode is no longer necessary.

Operate switch for wiper/washer system until windshield washer pump -V5- has been cycled for approx. 2 seconds.
Read display from display field.

Fig 12: Scan Tool Display -Display Field 4, Specified Value 30
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Specified value: "30" (requirement for recirculating air due to washer/wiper system, A/C switches for approx. 10 seconds to the recirculating air mode)
Wait a short period of time.
Read display from display field 4.
Specified Values: "00" (no requirement for "recirculating air, A/C in fresh air mode) or "60" (partial recirculating mode)

Fig 13: Scan Tool Display -Display Field 4, Specified Value 00
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NOTE:

Depending on the composition of the windshield washer fluid, the sensor can determine impurities in the air and request for "Automatic air recirculation."
If when activating the wiper/washer system the mode does not switch over to recirculating air, check the wiring connection between A/C control head -E87- and wiper/washer intermittent relay -J31- according to the wiring diagram.

Press --> button.
Indicated on display

Fig 14: Scan Tool Display - Select Function XX

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Push buttons -0- and -6- to select "End Output" function 06.
Indicated on display

Fig 15: Scan Tool Display - 06, End Output

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Press -Q- button to confirm input.
Indicated on display:

Fig 16: Scan Tool Display - Insert Address Word XX
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Switch ignition off and disconnect Data Link Connector (DLC).

NOTE:

If the function of the sensor for air quality -G238- is OK for this test and there is a customer complaint continue as follows:

Check dust and pollen filter for dirt.
Close DTC unit and select "Read Measuring Value Block" function 08.
Drive vehicle to area with relatively clean recirculating air (the system works in fresh air mode).
Now drive vehicle into an area with heavily polluted recirculating air (for example, on a street with construction or and truck traffic).

Display field 4, display group 001 must change from 00 or 60 to 10 when driving through a diesel exhaust cloud.

Read the notes. See SENSOR FOR AIR QUALITY -G238-, FUNCTION .