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Component Tests and General Diagnostics






Air Quality Sensor, Checking

- With the ignition switched off, connect the Vehicle Diagnosis, Testing And Information System (VAS 5051 A) with the Diagnostic Cable - 3 Meter (VAS 5051/5A) to the 16-pin data link connector on the vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

- Start the engine.

- Check the DTC memory of the Climatronic Control Module (J255) front A/C control head vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

- Set operating mode "Auto" on front A/C control head Climatronic Control Module (J255).

- Switch on the "automatic air recirculation" function via the front A/C control head Climatronic Control Module (J255) (function is displayed on screen of Multi Media Interface).

- Wait 30 seconds (warm up time for Air Quality Sensor (G238)).

- Select "Read measuring value block" on the Vehicle Diagnosis, Testing And Information System (VAS 5051 A). 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 (G238) and to the position of the recirculation flap vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• The A/C system operating condition (position of the recirculating/fresh air flap) and the condition of the signal from the Air Quality Sensor (G238) are displayed. Explanation of the possible displays vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• Specification: no request for "Recirculating air mode" present, (air conditioning in fresh air mode)

Or

• Specification: 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 (G238) from the mount. Refer to => [ Air Quality Sensor ] Removal and Replacement.

- Allow a little bit of gas from the lighter flow past - B - from the top area - A - of the Air Quality Sensor (G238)





• If the Air Quality Sensor (G238) 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 (G238).

• There are different versions of the Air Quality Sensor (G238), each with different functions. Make sure the allocation is correct. .

- Read the display with the Air Quality Sensor (G238) measured value and the recirculating/fresh air flap position vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• The specified value for the recirculating and fresh air flap 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 (G238) measured value and the recirculating/fresh air flap position 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 (G238) measured value and the recirculating/fresh air flap position vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• Specification: (Requirement for "recirculating air mode" due to washer/wiper system, A/C switches for approximately 10 seconds to the air recirculating mode

- Wait briefly.

- Read the display with the Air Quality Sensor (G238) measured value and the recirculating/fresh air flap position vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

• Specification: no request for "automatic recirculating air mode " present, air conditioning in fresh air mode.

Or

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

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

• If no change over to the recirculation air mode occurs when operating the windshield wiper/washer system switch, check the function the information " wash windshield" is received via the Comfort data bus system from the Steering Column Electronic Control Module (J527)Vehicle diagnosis, testing and information system VAS5051 in the "Guided Fault Finding" function.

If the function of Air Quality Sensor (G238) is OK for this test and there is a customer complaint continue as follows:

- Check dust and pollen filter for dirt.

- Connect the tester and select the "Read measured value block " function vehicle diagnosis, testing and information system VAS5051 in the "Guided Fault Finding" function.

- Second person is required to read out values displayed whilst driving.

- Follow the safety instructions vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function.

- Read the display with the Air Quality Sensor (G238) measured value and the recirculating/fresh air flap position 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 system in fresh-air mode.

- Then drive vehicle into an area where the atmosphere is polluted onto an uphill road with lorry traffic.

- Read the displays with the Air Quality Sensor (G238) measured value and the recirculating/fresh air flap position vehicle diagnosis, testing and information system VAS 5051 in the "Guided Fault Finding" function. The display with the Air Quality Sensor (G238) measured value and recirculating/fresh air flap position must change, for example when driving through a cloud of diesel exhaust.

- Also note descriptions, refer to => [ Dust and Pollen Filter ] Description and Operation and => [ Air Quality Sensor Function ] Description and Operation Air Quality Sensor (G238).
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