The automakers will report March vehicle sales on Tuesday, April 3rd.
Note: There were 28 selling days in March 2018, up from 27 in March 2017.
From WardsAuto: U.S. Light-Vehicle Forecast: Sales Down Slightly; Inventory Declines to Match Demand
A Wards Intelligence forecast calls for U.S. automakers to deliver 1.60 million light vehicles in March. … The report puts the seasonally adjusted annual rate of sales for the month at 16.9 million units, higher than last year’s 16.7 million but slightly under last month’s 17.0 million.
emphasis added
Sales in March will probably be at the slowest sales rate since last August. After August, sales were boosted by the hurricanes.