However, the fall is less than the drastic decline posted for April.
The automaker sold 6,139 medium and heavy commercial vehicles — mostly trucks — in May, compared to 7,469 in the same month of 2016, a fall of 18%.
Sales of light commercial vehicles, mostly light pick-ups, rose to 2,932 from 2,406 in the previous year.
With this, the company has narrowed the decline seen in its total vehicle sales in the new financial year (that started in April) to 19%.
For the first two months of the ongoing financial year, medium and heavy commercial vehicle sales are down 30%.
Last month, the company reported a 30 percent decline in total sales at 7,083 units. In April, sales of heavy and medium commercial vehicles declined by 43 per cent to 4,525 units.