Air Quality Sensor G238, checking: Checking

WARNING: This page is about a different car, the 2008 Audi S4, 2008 Audi RS 4, and 2008 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

Remove plenum chamber cover.
With the ignition switched off, connect Diagnostic Operation System VAS 5051A using, for example, Diagnostic Cable - 3 Meter VAS 5051/5A and K-Lead Adapter Vas6017B VAS 6017B (or K-Lead Adapter VAS 6017A) to the 16-pin diagnostic socket in the vehicle → Diagnostic Operation System VAS 5051A, connecting and selecting functions .
Start engine.
Check DTC memory → Diagnostic Trouble Code (DTC) Memory, checking (function 02) .

On operating and display module, Climatronic Control Module J255, set "Auto" mode.

Fig 1: Identifying "Automatic Air Recirculation" Button

Courtesy of VOLKSWAGEN UNITED STATES, INC.

"Automatic air recirculation" button - A - pressed (LED in button - A - lights).
Wait 30 s to allow Air Quality Sensor G238 to warm up.

Fig 2: Locating Control Module Identification With Code Indicated On The Display

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Indicated on display of Diagnostic Operation System VAS 5051A :

Select function "08 - Reading measuring value block".

Indicated on display of Diagnostic Operation System VAS 5051A :

Fig 3: Identifying Prompt For Entering Display Group Appears In Display Zone & Input Keypad Appears In Display Zone

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Prompt for entering display group appears in display zone - 1 -.
Input keypad appears in display zone - 2 -.

Use input keypad in display zone - 2 - to enter desired display group number "014" → Overview of selectable display group numbers .
Confirm entry with Q key.
Read displays in zones "3" and "4".

NOTE:

Display field "4" indicates operating status of air conditioner (fresh-air or recirculated-air mode), whereas display zone "3" shows status of Air Quality Sensor G238 signal. Remarks on possible displays and

Specified value in display zone "4"

"00" (no request for "recirculated-air mode", air conditioner in fresh-air mode)

"60" ("partial recirculated-air mode", fresh-air and recirculated-air flap open)

Fig 4: Positioning Spray Attachment Of Test Gas Canister Over Air Inlet Of Air Quality Sensor G238 (With Version "1" Of Air Quality Sensor G238)

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Position spray attachment - A - of test gas canister over air inlet of Air Quality Sensor G238 - B - (with version "1" of Air Quality Sensor G238).

Fig 5: Positioning Spray Attachment Of Test Gas Canister Over Air Inlet Of Air Quality Sensor G238 (With Version "2" Of Air Quality Sensor G238)

Courtesy of VOLKSWAGEN UNITED STATES, INC.

Position spray attachment - A - of test gas canister over air inlet of Air Quality Sensor G238 - B - (with version "2" of Air Quality Sensor G238).
Press spray knob - C - of test gas canister for approx. 1 second.

NOTE:

There are different Air Quality Sensor G238 housings. Version "1" was installed at the start of production. This sensor is gradually being replaced by version "2", however the mode of operation is identical.
The test gas canister is filled with pure oxygen with a specific nitrogen oxide component.
The Air Quality Sensor G238 also reacts when exposed to cigarette smoke or cigarette lighter gas (gas is heavier than air, the Air Quality Sensor G238 must therefore be removed and turned round).

Read off display in zone "4".

Specified value:

"10" ("Automatic air recirculation mode" requested, request met, air conditioner switches to recirculated-air mode)

Wait briefly approx. 1 minute, depending on amount of test gas sprayed onto Air Quality Sensor G238).
Read off display in zone "4".

Specified value:

"00" (no request for "recirculated-air mode", air conditioner in fresh-air mode)

"60" (Partial recirculated-air mode)

NOTE:

To stop the recirculated-air/fresh-air flaps being switched too frequently, an Air Quality Sensor G238 request for "automatic recirculated-air mode" is applied for at least 25 s (minimum dwell time) even if the pollutant concentration in the air has decreased to such an extent that recirculated-air mode would no longer be necessary.

Activate windshield wash/wipe switch until Windshield Washer Pump V5 has conveyed fluid for approx. 2 s.
Read off display in zone "4".

Specified value:

"30" ("Recirculated-air mode" requested because of windshield washer system, air conditioner switches to recirculated-air mode for approx. 10 sec.)

NOTE:

The request for "recirculated-air mode" during windshield washer system operation is not implemented with all versions of the operating and display module, Climatronic Control Module J255.

Wait briefly.
Read off display in zone "4".

Specified value:

"00" (no request for "recirculated-air mode", air conditioner in fresh-air mode)

"60" (Partial recirculated-air mode)

NOTE:

Depending on the composition of the windshield washer fluid, the Air Quality Sensor G238 may detect air pollution and request "Automatic air recirculation".
If switching to recirculated-air mode does not take place on activating windshield wipe/wash switch, check operation of Wiper/Washer Intermittent Relay J31 if applicable ("windshield wash" information is received via the CAN-Bus comfort system from the Steering Column Electronic Systems Control Module J527) (Reading measuring value block, display group "018").

Proceed as follows if the Air Quality Sensor G238 functions properly in this test but a customer complaint has been received:

Check for contamination of dust and pollen filter.
Connect Diagnostic Operation System VAS 5051A for example and select function "08 Reading measuring value block" for air conditioner.
Enter display group number "014" and read off displays in zones "3" and "4".

NOTE:

A second person is required to read out the values displayed while driving.
Pay attention to safety precautions → Safety precautions .

Perform a test drive, starting in an area with a relatively clean ambient atmosphere (system operating in fresh-air mode) and then proceeding to an area where the atmosphere is polluted (e.g. uphill road with truck traffic).

NOTE:

The display in zones "3" and "4" in display group "014" must change, for example, on driving through a cloud of diesel emissions → Overview of selectable display group numbers .
Also pay attention to the notes on the dust and pollen filter → Dust and pollen filter with active-carbon-filter element and on operation of the Air Quality Sensor G238 → Air Quality Sensor G238 .