Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Air Quality Sensor -G238-, Checking: Notes
Different versions depending on the vehicle date of manufacture and A/C system version ("Basis" or "Convenience"). Refer to Air Quality Sensor -G238-, FUNCTION .
The Air Quality Sensor -G238- is only installed on vehicles with the "Convenience" A/C system.
The Air Quality Sensor -G238- and the Humidity Sensor in Fresh Air intake Duct -G657- need approximately two minutes until they reach their operating temperature after turning on the ignition. The function of the Air Quality Sensor -G238- and the Humidity Sensor in Fresh Air intake Duct -G657- is limited during the warm-up phase.
During the warm-up phase, the Air Quality Sensor -G238- malfunctions may occur under certain ambient influences. Only replace the Air Quality Sensor -G238- if the Air Quality Sensor -G238- is repeatedly appearing as faulty. If the malfunction indicator for the Air Quality Sensor -G238- changes from "static" to "sporadic" after switching the ignition off and then on again (waiting at least two minutes each time), then the Air Quality Sensor -G238- is OK and the DTC memory entry no longer needs to be monitored (erase the DTC memory) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
Special Tools and Equipment
- Vehicle Diagnostic Tester with the Vehicle Diagnosis System - Updated Cable - 3m:VAS5051/5A
- Commercially available gas lighter (for checking the Air Quality Sensor -G238-)
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.