Q: Transmission on 2001 Audi A6 Quattro

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Reverse works on level ground, however, if backing up hill will not back. Does this require new trans or some kind of adjustment and/or flush?
(1) Answer
If the transmission will not operate under the pressure of going up a hill the problem is most likely in the transmission unfortunately. I would first have someone with a scan tool that has Audi diagnostic capabilities plug in a scan tool and see if the transmission has any trouble codes stored. Have the transmission fluid level checked.