Hi Colin
I read your post with interest.
I own a 2020 S4 tdi which I’ve had since new, and has always been serviced by the main dealer. The warranty expired in March and it recently hit 60k miles. It’s been trouble free until 60k miles but since then it has been plagued with issues and all sorts of warning lights have been popping up, including an Ad blue system failure, gear box malfunction and drive system fault, as well as a squealing noise coming from the engine bay on start up- this is sporadic. The first issue to appear was the squealing noise and the other issues have followed. The faults generally clear once the vehicle is restarted and don’t happen at all when I disable the start stop system. It was in Audi for a diagnostic on Tuesday and I had a slightly confusing update from the dealer today.. the gear box needs to be replaced (planetary failure!) but this will be covered under goodwill (£11k!) but I’d have to pay the labour costs. However, they then said they could just clear the fault and I could see how it goes- earlier in the week they told me it wasn’t driveable..
Regarding the other issues, there is a fault with the alternator and this needs replacing (£1900) and apparently there is an ECU issue with the ad blue system- £2200 to sort. I’m wondering if the gearbox and ad blue warning lights are just computer glitches caused by a low battery as a result of the alternator fault?