Audi a6 9.0 Question please Help!!! :)?

A couple of things... when you unlock the car, if you turn the key more, the windows will come down automatically. If you are using the keyless, entry, then it was modified to do that. Oxygen SENSORS were replaced, not tanks. As for the battery issue, I am sensing it needs an alternator, because you mentioned that the light kicked on, and the voltmeter needle dropped. Is there a warranty from the "pre-owned place?" Generally it is 30 days. If there is, take it back and demand that they repair it, and reimburse you for the battery. Also, the year would help too. You should have had this car checked over by an independent VW/Audi tech prior to purchase though.