[Miguel]

pawn Код:

new
  key[3],
  Float:x, 
  Float:y,
  Float:z;

GetPlayerKeys(playerid, key[0], key[1], key[2]);
GetVehicleVelocity(GetPlayerVehicleID(playerid), x, y, z);
if(floatsqroot(x*x, y*y, z*z) < 0 && key[0] == KEY_DOWN)
{
  // reverse
}