Well done. Glad that it was traced to a sensor and not a more systemic mechanical problem. The moral is: When the vehicle is under warranty, make them fix it.

Looking at my '09 manual - i think the Oxygen sensor is the one that screws into the zorst... Item 21...
http://www.yamahascooterspares.co.uk/sp ... AUST&uid=0
http://www.yamahascooterspares.co.uk/sp ... 5555&uid=0
£232.86 ... bet ya glad you got that sorted under warranty...

Pheww that's expensive. I'm really surprised a sensor could cost that much. They fitted it this morning, even let me have the loan bike for free last week. Only downside was they were out of coffee cups so didn't get a free coffee this morning!.

Even more surprised, the muffler and protectors are over £900. An Akrapovic unit costs about £400 fitted.

Sounds like you have reasonable dealer support...
If its in warranty, always take it straight back... if its a little out of warranty they may well be able to help - free parts and charge labour etc...
Happy Scootin' well when it stops pissing down!