A device for diagnosing the loss of a connection to a ground (M) of an electronic control module (BCM) of a motor vehicle, noteworthy in that a first branch (B1) for connecting to the ground (M) includes: elements of unidirectional current conduction (Dd) mounted in parallel with a two-position switch (INT), the two-position switch (INT) being configured to toggle between a closed short-circuit position of the elements of unidirectional current conduction (Dd) and an open position of diagnostic of the loss of connection to the ground (M) of the electronic control module (BCM) on the first connecting branch (B1), and, elements for generating a current (Idiag) on the first connecting branch (B1).