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Windscreen washing, detailed description

Windscreen washing, detailed description

The washer system is located at the front of the left hand front wing. It comprises a fluid reservoir with two pumps and a level sensor. The washer nozzles are located on the bonnet. The function is controlled by the electrical centre in the engine compartment. If the washer fluid level is low a message is transmitted on the bus. The MIU generates an acoustic signal and a message is displayed on the SID.


If the washer fluid level is less than 1 litre SID displays a message and the headlamp washing function is blocked in order to save washer fluid.

Function, windscreen washing

When the windscreen washer stalk is pulled toward the steering wheel, the CIM (703) sends the bus message "Windscreen washer, stalk, active" ON, provided that the ignition is ON. This bus message is used by the UEC (342) to activate the windscreen washer relay (432). B+ voltage is supplied from pin 36 (F) of the UEC (342) to the windscreen washer pump, which starts and pumps washer fluid to the three nozzles.


At the same time as windscreen washing starts, the ACC unit signals to the recirculation vent motor to shut the vent thus avoiding the smell of washer fluid in the vehicle.

In vehicles fitted with the rain sensor the sensor activates the windscreen wipers, via REC and UEC after the completion of washing.

Windscreen wiping in conjunction with washing

At the same time as windscreen washing starts the UEC (342) activates relay 83 which energises the wiper motor (62F). The UEC (342) supplies B+ via pin 30 (F) to pin 4 on the wiper motor (62F). The wipers are active as long as washing continues. When washing ceases the wipers complete a few more strokes in order to dry the windscreen.

Number of extra wiper strokes relative to washing times:


• < 0.5 seconds = 3 extra strokes

• 0.5-2.0 seconds = 4 extra strokes

• > 2.0 seconds = 5 extra strokes


The UEC (342) uses the end position contact, which is built into the washer motor, to ensure that the number of extra strokes is correct. At speeds under 20 km/h an extra wiper stroke is carried out after 8 seconds. If the ignition is switched off before completion of a wiper stroke the UEC (342) continues to activate the motor until the wipers reach the parking position.