It's new enough to use the EOBD standard.I feel their pain.
The ST220 is a fairly old car now and newer diagnostic tools will probably not be able to access it properly. (If at all)
For a garage to simply blindly plug in the diagnostics and then say "computer says no, sorry m8" without actually poking their head under the bonnet for 5 minutes and doing some simple physical diagnostic checks is poor show.