Abstract: The invention proceeds from an on-board diagnosis unit for a motor vehicle for detecting a released mechanical connection between at least two fluidic lines (10, 11), having at least one first contact element (12, 13, 14) and at least one second contact element (15) which is spaced apart axially, of which contact elements (12, 13, 14, 15) at least one is provided for being deformed at least substantially elastically for making contact with at least one connecting point (16, 17, 18) of the mechanical connection. It is proposed that the on-board diagnosis unit has at least one third contact element (12, 13, 14) which is arranged spaced apart axially from the second contact element (15).