[PrawkC]

Debug your CarInfo[vehicleid][vOwner] and make sure that its set correctly
so do like

pawn Code:

public CheckOwner(playerid)
{
    if(IsPlayerConnected(playerid))
    {
        for(new i = 1; i < sizeof(CarInfo); i++)
        {
            printf("Car %d owner %s", i, CarInfo[i][vOwner]);
            new playername[MAX_PLAYER_NAME];
            GetPlayerName(playerid, playername, sizeof(playername));
            if(!strcmp(playername, CarInfo[i][vOwner], true))
            {
                PlayerInfo[playerid][pVehicle] = 1;
                return i;
            }
            else
            {
                PlayerInfo[playerid][pVehicle] = 0;
                return i;
            }
        }
    }
    return 1;
}