[CentOS] SD Card Reader not being recognized

># yum --enablerepo=centosplus update kernel
>
I tried this, but unfortunately it was unsuccessful:

[root at localhost ~]# yum --enablerepo=centosplus update kernel
Repository update already added, not adding again
Error getting repository data for centosplus, repository not found

I thought since I added in the whole "dag" repository that I should have 
a fairly complete set of install options to choose from. To get 
centosplus, do I have to add more repositories or something?

Dave