An electronic device for a motor vehicle including: a thermally conductive casing containing a printed circuit board and a heat-generating element mounted on the printed circuit board; the casing including a casing bottom on which the printed circuit board is mounted and including a cover opposite to the casing bottom, a plurality of cooling fins extending on the external surface of the cover from a rear end of the plurality of fins to a front end of the plurality of fins, the plurality of fins comprising a first group of fins and a second group of fins, each group (32, 34) of fins extending from the rear end to the front end, the rear end of the first group and the front end of the first group defining respectively an air inlet of the first group and an air outlet of the first group, the rear end of the second group and the front end of the second group defining respectively an air outlet of the second group and an air inlet of the second group, means provided to generate an air stream between the plurality of fins of the first group, the air stream being able to flow from the air inlet of the first group to the air outlet of the first group so as to allow a cooling of the plurality of fins of the first group, characterized in that the electronic device comprises at least one air deflector arranged with respect to the air outlet of the first group and is configured to orient the air stream to the air inlet of the second group so that the air stream can flow between the fins of the second group from the air inlet of the second group to the air outlet of the second group in order to allow a cooling of the fins of the second group. a thermally conductive casing containing a printed circuit board and a heat-generating element mounted on the printed circuit board; the casing including a casing bottom on which the printed circuit board is mounted and including a cover opposite to the casing bottom, a plurality of cooling fins extending on the external surface of the cover from a rear end of the plurality of fins to a front end of the plurality of fins, the plurality of fins comprising a first group of fins and a second group of fins, each group (32, 34) of fins extending from the rear end to the front end, the rear end of the first group and the front end of the first group defining respectively an air inlet of the first group and an air outlet of the first group, the rear end of the second group and the front end of the second group defining respectively an air outlet of the second group and an air inlet of the second group, means provided to generate an air stream between the plurality of fins of the first group, the air stream being able to flow from the air inlet of the first group to the air outlet of the first group so as to allow a cooling of the plurality of fins of the first group, characterized in that the electronic device comprises at least one air deflector arranged with respect to the air outlet of the first group and is configured to orient the air stream to the air inlet of the second group so that the air stream can flow between the fins of the second group from the air inlet of the second group to the air outlet of the second group in order to allow a cooling of the fins of the second group.