Q&A

The Instrument Clusters on Audis do go out. So I would start there, I have actually seen, first hand, the cluster set an ABS light, because the Power Train Computer uses the Cluster to talk to the ABS and if it does not see the ABS data, it triggers an ABS light, so start with the Instrument Cluster, which is pretty pricey and needs to be programmed. I have done this job personally at least 6-7 times.
Then see if you still have an ABS light that comes on, of course after you clear all the codes in all the systems, you need to diagnose the ABS failure, (which is commonly an ABS module) BUT, scan the data stream to be SURE!! If there is still no data output from the ABS module, then it is usually a failed power relay in side the module, meaning you need a new module.
As for the Oxygen Sensor code, what is the exact code? If it was a P0171 or P0174, this is NOT an Oxygen Sensor issue. Read this article I wrote about lean codes, because many, many techs get confused by this.

http://repairpal.com/OBD-II-Code-P0171-and-P0174