I only updated (not upgraded) using Apple’s Mac OS X 10.10.x updaters, no archive & install. All I can find in /System/Library/CoreServices is the diagnostics_agent (and yes, I made invisibles visible).
then as far as I am aware of and understand the process, the diagnostics should still be there. But Apple seems to be moving toward netbooting diagnostics. They may be phasing out on-disk diags? Can you netboot diagnostics over the internet?
