Senior Police Officer 2 Jovito Felix Parillo, of Central Police District-Station 3, said the grenade hit the metal frame of the glass panel of the Ford Balintawak showroom along EDSA near the corner of Seminary Road at 11:30 p.m.
No one was hurt in the blast. Vehicles also escaped damage.
According to Parillo, witnesses saw a man aboard a Monumento-bound passenger bus tossing an object in the direction of the showroom.
But witnesses could not remember the license plate of the passenger bus, which could possibly lead police in identifying the suspect.
Police said that the incident could be related to the robbery that took place at the same showroom several months ago.