Possible reasons for changes in the way the rain sensor works
The rain sensor may misread what is happening in the detection zone of its sensitive rain-sensor
surface ⇒ fig. 91 (arrow) and not work for a number of reasons; which include:
x Worn out wiper blades: Worn out wiper blades may leave a film of water or wiping streaks; this can
cause the wipers to run longer, to wipe more often, or to wipe continuously at high speed.
x Insects: Insects hitting the sensor may trigger the wipers.
x Salt streaks: Salt streaks on the windshield from winter driving can cause wiping more often or
continuously on glass that is almost dry.
x Dirt: Caked-on dust, wax, any other build-up 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 recalibrate 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. 92 In the engine compartment: Cap of the windshield washer fluid reservoir.
