Humidity Sensor: Service and Repair

Air Quality Sensor (G238) With Humidity Sensor In Fresh Air Intake Duct (G657)

• The Air Quality Sensor/Humidity Sensor In Fresh Air Intake Duct is available in different versions. In this vehicle, a sensor - A - is installed in which the air quality sensor - C - and the humidity sensor in fresh air intake duct - D - are combined in a single component. Refer to Electronic Parts Catalog.






• Sensor - A - (combination sensor with the air quality sensor and the humidity sensor in fresh air intake duct ) is a highly sensitive electronic component that can be damaged if it comes in direct contact with fluids, solvents, fuels and certain chemical compounds (for example, contaminants can enter through area - C - or - D -). The function of the humidity sensor in fresh air intake duct can be severely affected by direct contact with water so that correct moisture values can no longer be measured (briefly or permanently depending on the composition of the fluid). For this reason, do not install sensors that may have come into contact with these substances.

• Following removal, do not set down air quality sensor /humidity sensor in fresh air intake duct in areas where it could come into contact with solvents, fuels or certain chemical compounds (liquids or vapors).

Removing and Installing

- Switch off the ignition.

- Remove plenum chamber cover, refer to - A -






• To prevent water from running via intake shaft - C - into the A/C unit when plenum chamber cover - A - is installed, plenum chamber cover - A - must not be damaged. Plenum chamber cover - A - must be correctly and completely engaged in frame - D - of windshield. Refer to - B -

- Rotate the air quality sensor /humidity sensor in fresh air intake duct - A - approximately 90° and remove it from the fresh air intake - E -.






- Disconnect connector - B - from sensor - A -.

Terminal assignment in connector - B -

1 B+ (terminal 15)
2 Ground (terminal 31)
3 Signal wire to the Vehicle electrical system control module (J519).

• The signal emitted by the air quality sensor and the humidity sensor in fresh air intake duct cannot be evaluated by workshop equipment.

• The data of the air quality sensor and the humidity sensor in fresh air intake duct is evaluated by the vehicle electrical system control module and is transmitted via the data bus to the Climatronic control module (J255). Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function and.

• The measured values of the air quality sensor and the humidity sensor in fresh air intake duct are displayed in the "read measured values" function of the Guided Fault Finding of the Climatronic control module and the vehicle electrical system control module. For explanatory notes regarding the displays use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.