Air Quality Sensor (G238), Checking
Air Quality Sensor (G238), Checking
Special tools, testers and auxiliary items required
• Vehicle Diagnostic Tester
• Commercial gas lighter
• The Air Quality Sensor - A - requires approximately 2 minutes to reach the operating temperature after the ignition is switched on.
• During the warm-up phase, the function is limited and a malfunction message can occur under certain ambient conditions. Replace the Air Quality Sensor - 2 - only if the Air Quality Sensor is registered continually as faulty. If the malfunction display for the Air Quality Sensor changes after switching off the ignition and then switching it back on (wait at least 2 minutes) from "static" to "sporadic", the Air Quality Sensor is OK and it is no longer necessary to pay attention to the event memory entry (erase the event memory) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• Certain A/C system functions (for example, control of the "automatic recirculation mode") can be switched on and off via the MMI (Multi Media Interface) in the "A/C system" function in the "Car"/"Car systems" menu. The A/C system control can also be influenced via presettings in the MMI (Multi Media Interface) under the "A/C system" function in the "Car"/"Car systems" menu. Therefore, first check the presetting in the MMI in the case of a problem with these components. Refer to Infotainment/MMI operating instructions.
Test Prerequisites
- The vehicle is in an area with clean ambient air.
• Not near running engines, outlets of exhaust systems, etc.
- The engine compartment and the plenum chamber are clean.
• Not contaminated with oil or fuel.
- The engine compartment and the plenum chamber were not sprayed with cleaning agents or preservatives containing solvents
- "Automatic recirculating air mode" is switched on.
• It is possible to switch the "automatic recirculation mode" on or off via the "A/C" function in the "car"/"car systems" menu in the MMI (Multi Media Interface). Refer to Infotainment/MMI operating instructions.
Check the function
- Remove the air quality sensor. The electrical harness connector remains connected. Refer to => [ Air Quality Sensor (G238) with Humidity Sensor In Fresh Air Intake Duct (G657) ] Service and Repair.
- Start the engine.
- Set "Auto" mode on the Climatronic control module.
- Set "automatic recirculation mode" via the MMI (Multi Media Interface) in the Climatronic control module. Refer to Infotainment/MMI operating instructions.
• After a warm-up period of 2 minutes, the air quality sensor is ready for operation.
- Read out the event memory of the Climatronic control module (J255) , and select "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Read the measured values of the air quality sensor. The air pollution measured by the air quality sensor is displayed.
• Value for the NOx level (nitrogen oxide) and the CO level (carbon monoxide) in the air.
• Explanatory notes regarding the possible displays using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Allow a little bit of gas from the lighter - B - to flow past from the top area - A - of the air quality sensor.
• The air quality sensor will react to butane gas. Butane gas is heavier than air. Therefore, remove the air quality sensor and apply from above.
- Read the measured values of the air quality sensor.
• Target value: In the display fields, the measured values for the "CO level" change with respect to the initial value, thus indicating that the "CO level" in the air quality sensor is functioning properly and the air quality sensor electronics are evaluating the measured values correctly.
• The "NOx level" sensor currently cannot be tested with workshop equipment. However, if the air composition around the sensor changes, the displayed value for the "NOx level" also changes.
- Wait a short period time (approximately. 1 minute, depending on amount of test gas flowing into the sensor).
- Read the measured values of the air quality sensor.
• Target value: The measured values in the display fields will return to the initial values and by doing so, show that both sensors are working correctly, and that the sensor electronics evaluated the measured values correctly.
• Due to changed pollution values, it is possible that different values can be displayed than those by the first measuring.
- Read the display with the measured values for the A/C operating status (recirculation/fresh air operation).
• Target value: The display field will show that the A/C system is working in the fresh air mode.
• If a value deviating from the "fresh air mode" is displayed in the "Read measured values" function, there is already a request for recirculation mode (for example, due to a "maximum cooling output" request or a "manual recirculation mode" setting). Select an operating mode that does not require recirculation mode.
• If the "Read measured values" function shows that the air quality sensor has already requested "automatic recirculation mode", clean the plenum chamber if necessary or park the vehicle in an area with clean ambient air.
- Allow a little bit of gas from the lighter - B - to flow past from the top area - A - of the air quality sensor.
- Read the measured values of the air quality sensor.
- Read the recirculation/fresh air mode display.
• Target values: There is a request for recirculation mode and the A/C system is in recirculation mode.
• If the "Read measured values" function shows that the air quality sensor is requesting "automatic recirculation mode" but this request cannot be implemented because of a shut-off condition of the Climatronic control module (J255) , eliminate the cause for this shut-off condition.
• In order to avoid frequent shifting of the recirculated air/fresh air doors and the recirculation doors, the requirement of the air quality 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 recirculated air mode is no longer necessary.
- Wait a short period time (approximately 1 minute, depending on amount of test gas flowing into the sensor).
• Target values: There is no longer a request for recirculation mode and the A/C system is back in fresh air mode.
- Install the air quality sensor. Refer to => [ Air Quality Sensor (G238) with Humidity Sensor In Fresh Air Intake Duct (G657) ] Service and Repair.
If the function of Air Quality Sensor is OK for this test and there is a customer complaint continue as follows
- Check the dust and pollen filter for contamination. Refer to => [ Dust and Pollen Filter ] Service and Repair.
- Select "Read measured values" using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
• Second person is required to read out values displayed whilst driving.
Observe the safety instructions using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Read out the displays in the "Read measured values" function for the measured values of the air quality sensor and the recirculation/fresh air mode request.
- Drive the vehicle to an area with relatively clean ambient air.
• Target value: The system is in fresh air mode.
- Then drive vehicle into an area where the atmosphere is polluted (for example, onto an uphill road with lorry traffic).
• Target value: The displays in the different display fields must change, for example, when driving through a diesel exhaust cloud.
• Also read and heed the descriptions of the mode of operation of the air quality sensor / humidity sensor in fresh air intake duct. Refer to=> [ Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) ] Description and Operation.