// En 'OnGameModeInit':
SetTimer("RepairVehicles", 1000, true);


// Lo otro.
forward RepairVehicles();
public RepairVehicles()
{
    for(new i = 0; i < MAX_VEHICLES; i++)
    {
        if(IsValidVehicle(i))
        {
            new Health = GetVehicleHealth(i, Health);
            if(Health < 250.0)
            {
                SetVehicleHealth(i, 1000.0);
                RepairVehicle(i);
            }
        }
    }
}

SetTimer("checkVehicleHealth", 1000, 1); //va OnGameModeInit o OnFilterScriptInit

forward checkVehicleHealth();
public checkVehicleHealth()
{
    static iPlayer, iVehicleID, Float:fVehicleHealth;
    iPlayer = 0;
    #if defined _FOREACH_LOCAL_VERSION
    foreach(iPlayer:Player)
    #else
    for(;iPlayer<MAX_PLAYERS;iPlayer++) if(IsPlayerConnected(iPlayer))
    #endif
    {
        iVehicleID = GetPlayerVehicleID(iPlayer);
        GetVehicleHealth(iVehicleID, fVehicleHealth);
        if(fVehicleHealth < 250.0)
        {
            RepairVehicle(iVehicleID);
        }
    }
}