I've just had this on my A6 C7 auto. It was a leaking auto gearbox coolant valve that's let water/coolant into the wiring connecting the gearbox and ICU - seemingly a problem known by Audi for some time. If so, get it fixed quickly as a new mechatronics unit is up to £4k, and you can't get components for it, e.g. the connector, only the whole unit! Another example of mfrs fleecing it's customers.
Automatic gearbox malfunction message
in Audi A6 (C7) Forum
Posted
I've just had this on my A6 C7 auto. It was a leaking auto gearbox coolant valve that's let water/coolant into the wiring connecting the gearbox and ICU - seemingly a problem known by Audi for some time. If so, get it fixed quickly as a new mechatronics unit is up to £4k, and you can't get components for it, e.g. the connector, only the whole unit! Another example of mfrs fleecing it's customers.