Hi there if anyone knows the location of downstream sensor 2 on c7 2.0 tdi ultra engine code ddda I've checked the exhaust system and near to the ad blue tank no luck can't find it 😢 anyone can help with that any thoughts please 

Thank you in advance 

 

Is it near the cat? 

I've checked near the catalytic before and after no sign of nox sensor 2 I've checked everything it looks like there isn't nox sensor but I definitely know there must be 2 nox sensor before and after catalytic 

46 minutes ago, John wild said:

I've checked near the catalytic before and after no sign of nox sensor 2 I've checked everything it looks like there isn't nox sensor but I definitely know there must be 2 nox sensor before and after catalytic 

Hi its around the DPF, after I think, could be you have three of them some later models had that but I think they have given up with that one and carried on with two, if you plumb in your VIN on LLL carports it will drag up a diagram.

Steve.

7 hours ago, Stevey Y said:

Hi its around the DPF, after I think, could be you have three of them some later models had that but I think they have given up with that one and carried on with two, if you plumb in your VIN on LLL carports it will drag up a diagram.

Steve.

1 2 3 and 4 are exhausting temperature sensors 

A is the lambada sensor then B is nox sensor upstream 

So I couldn't find other sensor to the dpf I'm literally giving up ))))

20250917_161510.heic

12 hours ago, John wild said:

1 2 3 and 4 are exhausting temperature sensors 

A is the lambada sensor then B is nox sensor upstream 

So I couldn't find other sensor to the dpf I'm literally giving up ))))

20250917_161510.heic 1.28 MB · 1 download

Hi as I said they are always changing things, I changed the DPF on my Passat back in the summer the donor car was a year younger and had a DTSB engine, fine as mine is a DTSA which has two nox sensors, the unit came with sensors so happy days except where 2 was supposed to be was a blanking plug so I had to use my old 2 sensor, turns out they had trouble with the 2 sensor so on later models so they deleted it, now the tricky bit nearly all diagnostic software will tell you its the downstream thats gone even though you dont have one its the first sensor thats failing, also had it where I have replaced sensor 2 but the fault remains as sensor 1 can't correlate the information its getting from sensor 1, so when 1 was replaced the fault went away, two questions, what leads you to believe its sensor 2 and how many miles has the vehicle covered, unfortunately you can't always trust the diagnostic codes given and you have to read between the lines between the code and what you have on the engine physically.

Steve.

3 minutes ago, Stevey Y said:

Hi as I said they are always changing things, I changed the DPF on my Passat back in the summer the donor car was a year younger and had a DTSB engine, fine as mine is a DTSA which has two nox sensors, the unit came with sensors so happy days except where 2 was supposed to be was a blanking plug so I had to use my old 2 sensor, turns out they had trouble with the 2 sensor so on later models so they deleted it, now the tricky bit nearly all diagnostic software will tell you its the downstream thats gone even though you dont have one its the first sensor thats failing, also had it where I have replaced sensor 2 but the fault remains as sensor 1 can't correlate the information its getting from sensor 1, so when 1 was replaced the fault went away, two questions, what leads you to believe its sensor 2 and how many miles has the vehicle covered, unfortunately you can't always trust the diagnostic codes given and you have to read between the lines between the code and what you have on the engine physically.

Steve.

Thank you very much for response well I start from beginning i had issue with ad blue system recently I've had some tests regarding ad blue issue so I've got warning light on dashboard like ad blue system fault no restart within 600 m I've checked everything what can cause this warning light so at the end I've concluded it's nox sensor downstream which diagnostic tools showed it's not installed isn't reading any live data so as I'm concerned if the nox sensor downstream isn't working or is missing that could trigger the warning light on dashboard by the way no other fault codes found it

Thank you in advance 

On 11/4/2025 at 6:07 PM, John wild said:

Thank you very much for response well I start from beginning i had issue with ad blue system recently I've had some tests regarding ad blue issue so I've got warning light on dashboard like ad blue system fault no restart within 600 m I've checked everything what can cause this warning light so at the end I've concluded it's nox sensor downstream which diagnostic tools showed it's not installed isn't reading any live data so as I'm concerned if the nox sensor downstream isn't working or is missing that could trigger the warning light on dashboard by the way no other fault codes found it

Thank you in advance 

Hi thats better the fault you have has nothing to do with the nox sensor, its the level sensor in the adblue tank which if you fill it with the appropriate amount of adblue so its more or less full, then do a tank level sensor reset that should cure the problem, even if the nox sensor was there and had failed it would give a code to that effect but would give a zero reading on live data.

Steve.

8 hours ago, Stevey Y said:

Hi thats better the fault you have has nothing to do with the nox sensor, its the level sensor in the adblue tank which if you fill it with the appropriate amount of adblue so its more or less full, then do a tank level sensor reset that should cure the problem, even if the nox sensor was there and had failed it would give a code to that effect but would give a zero reading on live data.

Steve.

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 😊