Bosch SHE55P Repair Manual page 23

4.1.17.3 Top load dispensers
431413 top-load dispensers enable detergent and rinse-aid to be
added while doors are partially open (preferably @ 45º). The
dispensing mechanism uses a solenoid instead of an actuator
(wax motor).
The plastic linkage opens the detergent dispenser door when the
solenoid first operates, then cocks in place to dispense rinse-aid
when the solenoid operates again. After the 2nd operation, the
linkage resets for the next wash.
Rinse-aid dosage is shown on the digital display and is changed
through the dishwasher controls, not through a dispenser dial.
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4.1.18 Aqua sensor
The aqua sensor is located behind the sump, to the left of the
heater. It's a two-piece assembly, with a small circuit board in a
plastic housing). It senses water cleanliness and allows the
dishwasher control to remove pre-wash and/or pre-rinse cycles to
save energy (~ 20% energy savings).
.
If water is clean enough, it will be kept for the wash cycle. If not,
the aqua sensor directs the dishwasher to add an additional pre-
rinse or pre-wash cycle.
Dishwashers still operate adequately when aqua sensors fail.
Customers will only notice aqua sensors failing if they see their
dishwashers running slightly longer or their electric and water
usage getting slightly higher.
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