Hi Steve I did fill it up I've had reset scr sensor and scr lock but no luck I've checked the ad blue sensor it's working fine even i asked the specialist from audi he said if the nox sensor 2 downstream doesn't give you live data that definitely could be the issue which can cause the warning light on dashboard so that's why I was wondering if I'll find the nox sensor 2 I may be able to fix the problem but unfortunately on this car seems to be doesn't have one I've got Audi A6 c7 ultra 2017 engine code it's DDDA I've looked on manual the nox sensor 2 it's supposed to be near to ad blue tank but the isn't any sensor at all so I gave up and I booked an appointment for audi dealer to fix the problem I'll keep you posted
have a good day 😊