It's a normal practice for Honda dealers to charge $ for diagnostics on items that are covered under Warranty?

I ask because my Accord (103k) has the SRS light on. I checked the code and it’s the 15-3 OPDS sensor. I reset the OPDS last week as my Service Manual suggest. But it came back on this week. The OPDS sensor is covered under extended warranty (Recent Bulletin) for 10yrs 150K. I told the problem to the dealer and they told me they will have to charge $85 to diagnose the problem and if it is a 15-3 they will repair free of charge under warranty but I still have to pay for diagnostic.

Should I report them to Honda Motor Co.? Any recommendations?