wiper size VOLKSWAGEN PASSAT 2009 Owners Manual

x Dirt: Caked-on dust, wax, any other buildup on the windshield (lotus effect), or car-wash detergent residue can lower the rain sensor's sensitivity and cause it to react too slowly or not at all.
x Crack or chip in the windshield: If a stone hits and chips the windshield while the rain sensor is on, this will trigger a wiper cycle. After that, the rain sensor will recognize the change and re-calibrate itself to respond to the sensitive surface's reduced detection zone. Depending on the size of the chip, the sensor's reaction pattern may or may not change.
WARNING
The rain sensor cannot always recognize rain and activate the wipers.
x Switch the wipers on manually when water on the windshield reduces visibility.
Clean the rain sensor's sensitive surface (arrow) regularly and check the wiper blades for wear or damage.
To remove wax and coats of polish safely, we recommend using an alcohol-based windshield cleaner.
Checking and refilling windshield washer fluid

Fig. 107 In the engine compartment: Cap of the windshield washer fluid reservoir.