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Air Quality Sensor (G238), Checking






Air Quality Sensor (G238), Checking

Special tools, testers and auxiliary items required

• Vehicle Diagnostic, Testing and Information System (VAS 5051 A) with Diagnostic Cable (VAS 5051/5A)

• Commercial gas lighter

Test Requirements

• Vehicle standing in a clean atmosphere (away from running engines, exhaust vents, etc.)

• Engine compartment and plenum chamber clean (not contaminated with oil or fuel)

• Engine compartment and plenum chamber not sprayed with cleaning agents or preservatives containing solvents

Checking

- With the ignition switched off, connect the (VAS 5051 A) with the (VAS 5051/5A) to the 16-pin data link connector on the vehicle, refer to Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.

- Start the engine.

- Check the DTC memory of the Climatronic control module (J255) using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.

- Set operating mode "Auto" on Climatronic control module.

- Switch on the "automatic air recirculation" using the Climatronic control module (will appear in the MMI display). Refer to the Owner's Manual and Owner's Manual / Infotainment/MMI.

- Wait 30 seconds (warm up time for Air Quality Sensor).

- Using the (VAS 5051 A) select "Read Measured Value Block", the associated display group on the Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.

- Read the displays with the signal from the air quality sensor and to the position of the recirculation door using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.

• The A/C system operating status (position of the recirculating/fresh air door) and the status of the signal from the Air Quality Sensor are displayed. Explanation of the possible displays on the Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.

• Specified value: no request for "Recirculating air mode" present, (A/C system in fresh air mode)

Or

• Specified value: no request for "automatic recirculation mode" present, request for "partial recirculation mode" present (fresh air/recirculating door in the center position)

- Remove the air quality sensor from the mount, refer to => [ Air Quality Sensor ] Air Quality Sensor (G238).

- Allow a little bit of gas from the lighter flow past - B - from the top area - A - of the air quality sensor.






• If the air quality sensor comes in contact with cigarette smoke or with gas from an ignitor, it will react since ignitor gas is heavier than air; remove the air quality sensor.

• There are different versions of the air quality sensor, each with different functions. Make sure the allocation is correct using the Electronic Parts Catalog.

- Read the display with the air quality sensor measured value and the recirculating/fresh air door position using Vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• The specified value for the recirculating and fresh air door position changes from fresh air or partial recirculation mode when there is a request for "automatic recirculation mode". The request is fulfilled (the A/C system switches to recirculation mode).

- Wait a short period time (approximately 1 minute, depending on amount of test gas sprayed in sensor).

- Read the display with the air quality sensor measured value and the recirculating/fresh air door position using the vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• The specified value for the recirculating/fresh air flap position changes from recirculation mode to fresh air or partial recirculation mode (no request for "automatic recirculation mode" present, A/C system in fresh air or partial recirculation mode).

• In order to avoid frequent shifting of the recirculating air/fresh air door, the requirement of 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 recirculating air mode is no longer necessary.

- Operate switch for wiper/washer system until Windshield Washer Pump (V5) has delivered fluid for approximately 2 seconds.

- Read the display with the air quality sensor measured value and the recirculating/fresh air door position using vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• Specified value: Request for "Recirculating Air Mode" due to washer/wiper system, A/C system switches for approximately 10 seconds to the air recirculating mode.

- Wait briefly.

- Read the display with the air quality sensor measured value and the recirculating/fresh air door position using vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• Specified value: no request for automatic recirculating air mode present, A/C system in fresh air or partial recirculating air mode.

• Depending on the composition of the windshield washer fluid, the air quality sensor can determine impurities in the air and request for automatic air recirculation.

• If no changeover to recirculating air mode occurs when operating switch for windshield wiper/washer system, check function (the information Wash Windshield is received via Comfort CAN-Bus system), check using Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.

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

- Check dust and pollen filter for dirt, refer to => [ Dust and Pollen Filter ] .

- Connect the scan tool and select the "read measuring values block" using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".

- Since the displayed values are read out while vehicle is driven, a second mechanic is required (observe safety precautions for Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" function.

- Select the display group with the measured values for the air quality sensor and for the recirculating/fresh air door position using Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.

- Start by driving vehicle into an area with a relatively clean atmosphere (A/C system is working in fresh-air mode).

- Then drive vehicle into an area where the atmosphere is polluted (for example, onto an uphill road with lorry traffic).

- Read the display with the measured value for the air quality sensor and for the recirculating/fresh air door position. The display must change, for example when driving through a diesel gas cloud (for example, from fresh air mode to "Automatic Air Recirculation") using Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function.

- Also note descriptions of dust and pollen filter, refer to => [ Dust and Pollen Filter with Activated Charcoal Filter Unit ] Description and Operation and functions of air quality sensor by referring to => [ Air Quality Sensor Function ] Description and Operation.

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