Seeing that your DIYer tool had detected speed sensor stored fault/codes, I doubt your problems are over with an Oxygen Sensor change..
Hope they are , but the two are not in the same bag and I for one will be surprised if codes do not re-appear in a few days.
At least the Dealer has guaranteed this as a solution, so you have that to work with..
A stored fault code can be a trying diagnosis , but I can assure you that there are many, many DIYers here that have saved a small fortune by retrieving codes, chasing the possibles , asking ,listening, and investigating the problem with the help of this group... and , believe it or not, solving the problem.
Good luck.