Abstract: The invention relates to a motor vehicle wiping unit (1) comprising: at least one motor (2) configured to drive at least one windscreen wiper (5, 6) in a to-and-fro movement over a motor vehicle glass surface (11), at least one reduction gear (3) arranged at the output of the motor (2), and a controller (4) configured to determine a command for the motor (C), characterized in that the controller (4) is configured to determine the command for the motor (C) by taking into account at least one variable parameter linked to the efficiency of the reduction gear (3) such as to counterbalance the variation in the efficiency of the reduction gear (3) by changing the electrical power to be provided to the motor (2). The present invention also relates to a method for commanding the rotational speed of a motor for driving at least one windscreen wiper in a to-and-fro movement over a motor vehicle glass surface.