Climate Control Exhaust Gas Sensor: Testing and Inspection
Air Quality Sensor (G238)/Humidity Sensor in Fresh Air Intake Duct (G657), Checking
Special Tools and Equipment
• Vehicle Diagnostic Tester with diagnostic cable (VAS 5051/5A)
• Commercially available gas lighter (for checking air quality sensor)
• There are different versions depending on the vehicle date of manufacture and which A/C system ("Basis" or "Comfort") is installed. Refer to => [ Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) Function ] Description and Operation.
• The air quality sensor is installed only on vehicles with the "Comfort" A/C system.
• The humidity sensor in fresh air intake duct is only installed on vehicles from MY 12 as a running change. Refer to => [ Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) Function ] Description and Operation.
• The air quality sensor and the humidity sensor in fresh air intake duct need approximately 2 minutes to reach their operating temperature after turning on the ignition. The function of the air quality sensor and of the humidity sensor in fresh air intake duct is limited during this warm-up phase.
• During the warm-up phase, air quality sensor malfunctions may occur under certain ambient conditions. Replace the air quality sensor only if the air quality sensor is repeatedly appearing as defective. If, switching the ignition off and then on again, (waiting at least 2 minutes) the air quality sensor malfunction display changes from "static" to "sporadic", then the air quality sensor is OK and the and the malfunction entry no longer needs to be monitored (erase the DTC memory) using the Vehicle diagnostic tester in "Guided Fault Finding".
• The function of the humidity sensor in fresh air intake duct can only be checked via the "Guided Fault Finding". The measured values of the humidity sensor in fresh air intake duct are evaluated via the "read measured values" function and compared to the temperature and humidity measured at the installation location of the humidity sensor in fresh air intake duct. Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
Test Requirements
• Vehicle standing in a clean atmosphere (away from running engines, exhaust vents, etc.)
• 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 recirculating air mode" on or off via the "A/C System" in the "Car" menu in the MMI (Multi Media Interface). Refer to the Infotainment / MMI Operating Instructions.
• Check the function of the humidity sensor in fresh air intake duct. Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
Checking
With High Voltage Systems (hybrid vehicles)
Read and follow all of the supplemental warnings for all work performed on vehicles with the high voltage system.
If it is necessary for the following procedure to perform work in the vicinity of high voltage components, perform a visual inspection of the high voltage components and cables for damages, refer to => [ Visual Inspection of High-Voltage Components and Cables for Damage ] Visual Inspection of High-Voltage Components and Cables For Damage and always follow the warnings when working on the high voltage system.
Risk of unintended engine start
The ignition must be turned off and the ignition key must remain outside of the vehicle when working on vehicles with a high voltage system.
How to handle high voltage cable:
• Do not stand on or place tools on high voltage cables and their components as it may damage the cable insulation.
• Never bend or kink high voltage cables forcefully as it may damage the cable insulation.
• Color-code the round high voltage connector with an external color ring and code them mechanically using the guide- or code tabs. Always make certain that the coding matches when connecting the round connector in order to avoid mechanically damaging the high voltage connector.
There is a risk of electrocution from damaged high voltage components
Observe the following when working around high voltage components and high voltage wires:
• Never work around high voltage components and cables with cutting, deformed, or sharp edged tools, or heat sources such as welding or soldering tools, heated air, and thermal glue.
• Inspect the high voltage components visually before beginning.
• Perform a visual inspection of the electric drive power and control electronics (JX1) , the electro-drive drive motor (V141) , the A/C compressor (V470) and the high voltage lines when working in the engine compartment.
• Perform a visual inspection of the high voltage lines and the cover when working on the underbody.
• Perform a visual inspection of the high voltage lines and the Electrobox with the high voltage system maintenance connector (TW) when working in the luggage compartment.
• Perform a visual inspection on all of the potential equalization cables.
Observe the following items when performing the visual inspection:
• The components do not display any signs of external damage.
• The high voltage cable insulation and the potential equalization cables are not damaged.
• The high voltage cables do not display any abnormal deformations.
• Every high voltage component is marked with a red warning label.
- Turn off the ignition.
- Remove the rubber seal - A - and the plenum chamber cover - B - (there are different versions).
• Inspect the high voltage components - D - (the electric drive power and control electronics (JX1) ) and the high voltage cables - E - after removing the plenum chamber cover - B -. Refer to => [ Visual Inspection of High-Voltage Components and Cables for Damage ] Visual Inspection of High-Voltage Components and Cables For Damage.
• Be careful not to damage any high voltage components - D - or the high voltage cables - E -.
• Inspect the high voltage components - D - and high voltage cables - E - after completing the work procedure and before installing the plenum chamber cover - B -.
Working on a high voltage system when activated or with the ignition turned on
The engine may start unexpectedly when performing work while the ignition is turned on or when the ready mode is activated and may cause poisoning in enclosed spaces. Be aware of body limbs and/or clothing when clamping or pulling.
Perform the following steps before turning on the ignition:
• Move the selector lever into position P
• Activate the parking brake
• Switch off ignition.
• Open the engine hood
• Connect a charging unit such as (VAS 5093) to the battery jump start terminal for the 12V vehicle electrical system
• Switch on the ignition
- Charge the vehicle battery using the (VAS 5903) in the battery support mode to minimize the number of automatic starts during the test- and measuring procedures while the ready mode is active.
- Move the selector level into position "P", activate the parking brake and arrange the necessary tools for testing and measuring procedures that require the ready mode to be active or that require the ignition to be on, so that they cannot come into contact with the turning components in the engine and so that they are not in the vicinity of the turning components of a running engine.
• Also move the selector lever into position "P" and activate the parking brake for testing and measuring procedures which require the ignition to be on, but do not require the ready mode to be active.
• The ready mode is displayed in the instrument cluster control module (J285) above the "power meter". Refer to the Owners Manual.
• Activate and deactivate the ready mode. Refer to the Owners Manual (consult the display in the instrument cluster control module).
Without A High Voltage System
- Turn off the ignition.
- Pull the left rubber seal - B - as far as necessary.
- Remove the fresh air intake cover on the wind cowl - A - or the wind cowl (different styles).
• If necessary, carefully loosen the wind cowl from the windshield cross member - C -.
All vehicles
- With the ignition switched off, connect the Vehicle Diagnostic Tester with Diagnostic Cable - 3 Meter (VAS 5051/5A) to the 16-pin Data Link Connector (DLC) of vehicle and perform the self diagnosis using the Vehicle diagnostic tester in "Guided Fault Finding" function.
- Turn on the ignition (vehicles with the high voltage system).
- Start the engine (vehicles without the high voltage system).
• The vehicle electrical system may turn off the engine on a vehicle with the Start/Stop System.
- Check DTC memory of the Climatronic control module (J255) using the Vehicle diagnostic tester in "Guided Fault Finding".
- Set the Climatronic control module to "Auto" ("Comfort" system).
- Using the MMI (Multi Media Interface) set "automatic recirculating air mode" in the Climatronic control module display and control head (refer to => Infotainment / MMI operating instructions ).
- Wait 2 minutes. ( Air Quality Sensor (G238) warm-up time).
- Using the Vehicle diagnostic tester select "read measured values block" and then read the measured values for the air quality sensor using the Vehicle diagnostic tester in "Guided Fault Finding".
• The NOx- portion (nitrogen oxide) and the CO- portion (carbon monoxide) in the air measured by the air quality sensor is displayed in the measured values block; explanation for possible displays using the Vehicle diagnostic tester in "Guided Fault Finding"
- Rotate the air quality sensor - A - approximately 90° to the left and remove it from the fresh air intake - C -.
- Allow a little bit of gas from a lighter - B - to flow past 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 igniter, it will react since igniter gas is heavier than air. Remove the air quality sensor.
- Select and read the air quality sensor measured values using the Vehicle diagnostic tester in "Guided Fault Finding".
Target values:
• The measured values increase contrary to the output value and show that both sensors in the air quality sensor are working correctly and the measured values are correctly evaluated.
- Wait a short period time (approximately 1 minute, depending on amount of test gas flowing into the sensor).
- Read the air quality sensor measured values.
Target values
• The measured values will return to the output 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 values
• The display field will show that the A/C is working in the fresh air mode.
• If a deviating value from the "fresh air mode" is displayed in the measured values block, then there is already a request for recirculating air mode (for example, due to the request for "maximum cooling output" or "manual recirculating air mode)" select a setting that does not require recirculating air mode.
• If it appears in the measured values block that the air quality sensor is already requesting automatic air recirculation, then, if necessary, clean the plenum chamber or move the vehicle into an area where the air is cleaner. Check using the Vehicle diagnostic tester in "Guided Fault Finding".
- Allow a little bit of gas from a lighter - B - to flow past from the top area - A - of the air quality sensor.
- Read the recirculation/fresh air mode display.
Target values
• In the measured values block, it will be displayed that a request for air recirculation is present and that the A/C system is working in the air recirculation mode.
• If it shows in the measured values block that the air quality sensor has requested automatic air recirculation, this request will not be performed based on a shut-off requirement from the Climatronic control module. Repair cause for this switch off condition. Verify using the Vehicle diagnostic tester in "Guided Fault Finding".
• 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).
• If the measured value block shows that there is no longer a request for air recirculation, then the A/C system is working again in the fresh air mode.
If the function of Air Quality Sensor (G238) is OK for this test and there is a customer complaint continue as follows:
- Check the dust and pollen filter for soiling. Refer to => [ Dust and Pollen Filter ] Service and Repair.
- With the ignition switched off, connect the Vehicle Diagnostic Tester with Diagnostic Cable - 3 Meter (VAS 5051/5A) to the 16-pin Data Link Connector (DLC) of vehicle and perform the self diagnosis using the Vehicle diagnostic tester in "Guided Fault Finding"
- Using the Vehicle Diagnostic Tester select "Read measured value block" using the Vehicle diagnostic tester in "Guided Fault Finding".
• Second person is required to read out values displayed whilst driving.
Always pay attention to the safety instructions when using the Vehicle diagnostic tester in "Guided Fault Finding"
- Read the displays in the measured value block for the air quality sensor values and the recirculation/fresh air mode request.
- Drive the 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 (for example, onto an uphill road with truck traffic).
- Read the displays in the different display fields. The displays in the different display fields must change; for example, when driving through a diesel exhaust cloud.
• Pay attention to the descriptions => [ Dust and Pollen Filter ] Service and Repair and => [ Air Quality Sensor (G238) and Humidity Sensor in Fresh Air Intake Duct (G657) Function ] Description and Operation.