Charging for fault investigations, including warranty work is unfortunately standard practice at most franchised garages now. It is, I guess designed to ensure garages are paid for their time where there is no valid warranty claim, but also reflects the investment in technical equipment necessary for analysis. I think to put all of this into perspective, these instances are extremely rare. Having owned 8 new Hondas since 1994, I have never had a problem, and I have had warranty repairs, dealt with as expected. If the warranty claim is valid, I am sure any costs would be refunded. If not, then clearly somebody has to pay.