dishwasher pump runs continuously

Recently I got a failure in my Bosch dishwasher.
The dishwasher pump runs continuously despite there's no water in the machine and even when I opened the door. My father ìn law knew what the problem was and he fixed it.
Someone sent me the following link to a service training manual:
http://www.cteq.ca/Doc_texte/Dishwash...
For those who want to do a thorough cleaning job, see reply of cvandoren1 below!

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