Where is the BMW moisture sensor located?
3 Answers
At the air intake of the car's air conditioning system. Below is relevant information about automotive air conditioning: Air conditioning layout: Different types of air conditioning systems have varying layout methods. Currently, most passenger cars widely adopt integrated heating and cooling air conditioning systems. The layout typically involves assembling components such as the evaporator, heater core, centrifugal blower, and control mechanisms together, collectively referred to as the air conditioning unit. Air conditioning components: Modern air conditioning systems consist of refrigeration systems, heating systems, ventilation and air purification devices, and control systems. Automotive air conditioning systems generally include components such as the compressor, electronically controlled clutch, condenser, evaporator, expansion valve, receiver-drier, pipelines, condenser fan, vacuum solenoid valve, idle speed controller, and control system. Automotive air conditioning systems are divided into high-pressure and low-pressure lines. The high-pressure side includes the compressor output side, high-pressure lines, condenser, receiver-drier, and liquid lines; the low-pressure side includes the evaporator, accumulator, return lines, compressor input side, and compressor oil sump.
On BMW vehicles, the humidity sensor is typically installed on the upper inner side of the windshield, near the base of the rearview mirror. This is not a sensor in the traditional sense, but actually part of the rain sensor system, which uses infrared light to detect the state of raindrops on the glass. This positioning is designed for convenient signal transmission and to avoid external interference—for instance, it must be in close contact with the inner surface of the glass, otherwise its sensitivity may decrease. In daily use, if the area gets contaminated with oil or dust, the automatic wiper function might malfunction, so I often remind car owners to gently wipe this area during car washes. When replacing it, be careful not to apply excessive force to the glass to prevent cracks. Remembering its location can help quickly diagnose issues—if the wipers aren’t working properly, check here first to ensure it’s clean, preventing minor issues from turning into major problems.
When I first bought a used BMW, I noticed the automatic wiper mode kept malfunctioning. Later, I learned that the moisture sensor is located at the top of the windshield, near the rearview mirror. Before each rain, I simply check that area for any debris buildup—it's quite visible, and you can easily see it by slightly bending down. This sensor mainly helps the system determine the moisture level, ensuring the wipers operate just right. If it stops working, the risk while driving in the rain is quite high, so I suggest friends develop a habit of checking dashboard warnings. The position is fixed and similar across different BMW models, making it convenient to learn some DIY basics, but if you lack experience, it's best not to tamper with the glass part.
