Take it to the official agency, if it continues in guarantee, if it is not in the usual, in another, but insists because the ruling looks electronic and if it is not with the diagnostic device, they cannot look at you what is failing.
It may be that the device diagnoses the failure in one thing and when changing it nothing, (which is what has sure happened to them) but in this case I tell you, when the same error appears again and again, it is because either the wiring that goes to the piece that is supposed to be wrong, or the reflected fault is a chain reaction, for example, if it jumps the oxygen sensor it may not be the eg Catalizer, the flowmeter or engine temperature sensor.
If the car guarantee has happened to you, all these tests are translated into money and insulous excuses as \ "no, you had this piece broken too and we have changed it \" o \ "is that these cars all come out with this defect ... \"
pay attention to me, while you have guarantee even if you have to be at the door of the agency giving war.
All the best. And hopefully the cause of such tremendous headache is nonsense.