I had this problem with my SC 815,  it came up with the EEE, after 3
times it locks out, and doesn't even say EEE.  I don't know if this
helps, but what happened was the code was changed and the original
owner, nor I knew it. So I called a Volvo Dealership and they said to
pull out the radio and read them the serial numbers on it, and they
could look it up in their computer system if it was a code issue

The radio is easy to pull out, there's a tab on each side, bottom left
and right, push in with pen or pencil tip and the tab will pop out.
Then pull the radio out and the serial number will be there.

However when I went to do this, the new "Code" was written there, right
in plain sight! So much for a theft proof system! It worked fine after
I punched it in.