Hello, i have a 2012 Audi a3 2.0 tdi I have had a p0401 code on for awhile now and finally decided to test into it as the car was running fine so it wasn’t an immediate issue for me. Well after evaluating I took the egr valve off tested it and it worked fine and wasn’t super plugged up so I cleaned the little soot that was on it and put it back in. Also put new engine air filter in and replaced the egr differential pressure sensor. After driving about 90 miles the cel turned back on for the p0401 code again. After reading some things I was going to take the egr filter off next and clean that was wondering if there’s anything else I should check I really don’t want to tear into the cooler at all if I have to do that I will probably just end up deleting the egr all together.

any suggestions would be awesome thank you 

Edited December 18, 2025Dec 18 by Tpowlowski28

30 minutes ago, Tpowlowski28 said:

Hello, i have a 2012 Audi a3 2.0 tdi I have had a p0401 code on for awhile now and finally decided to test into it as the car was running fine so it wasn’t an immediate issue for me. Well after evaluating I took the egr valve off tested it and it worked fine and wasn’t super plugged up so I cleaned the little soot that was on it and put it back in. Also put new engine air filter in and replaced the egr differential pressure sensor. After driving about 90 miles the cel turned back on for the p0401 code again. After reading some things I was going to take the egr filter off next and clean that was wondering if there’s anything else I should check I really don’t want to tear into the cooler at all if I have to do that I will probably just end up deleting the egr all together.

any suggestions would be awesome thank you 

Hi you have replaced most of the relevant parts, easy check wipe the inside of the tail pipe if you get a load of soot on your fingers the DPF is cracked that will throw that code also when you replaced the pressure sensor did you re adapt the new unit. 

Steve.

1 hour ago, Stevey Y said:

Hi you have replaced most of the relevant parts, easy check wipe the inside of the tail pipe if you get a load of soot on your fingers the DPF is cracked that will throw that code also when you replaced the pressure sensor did you re adapt the new unit. 

Steve.

Hi Steve yes the tail pipe has soot in it and I’m willing to bet my dpf is definitely cracked but I was just trying to get the light to clear so I can pass a inspection (I’m in New York) also I didn’t re adapt the new unit I also had the throttle body out from when I took the egr valve out should I re adapt that as well as it has a part in the regen process? I was just looking into getting vcds to be able to do those things. 

Edited December 18, 2025Dec 18 by Tpowlowski28

20 hours ago, Tpowlowski28 said:

Hi Steve yes the tail pipe has soot in it and I’m willing to bet my dpf is definitely cracked but I was just trying to get the light to clear so I can pass a inspection (I’m in New York) also I didn’t re adapt the new unit I also had the throttle body out from when I took the egr valve out should I re adapt that as well as it has a part in the regen process? I was just looking into getting vcds to be able to do those things. 

Hi VCDS is the best possible thing you could buy, I have it and despite its price its amazing the support site is beyond helpful, on your year of Audi there wont be anything you can't adapt or reprogram, I personally would adapt everything you have moved or cleaned/replaced, it should also put the light out, just take it with you when you go for your inspection and if the light is on clear it before the inspection as it is unlikely to return immediately as all these faults require a certain amount of drive cycles before the ECU cottons on to the fact the fault is still there, you may well find that a relearn on the pressure sensor cures it but either way it will buy you time to decide what you want to do.

Steve.

On 12/19/2025 at 2:38 PM, Stevey Y said:

Hi VCDS is the best possible thing you could buy, I have it and despite its price its amazing the support site is beyond helpful, on your year of Audi there wont be anything you can't adapt or reprogram, I personally would adapt everything you have moved or cleaned/replaced, it should also put the light out, just take it with you when you go for your inspection and if the light is on clear it before the inspection as it is unlikely to return immediately as all these faults require a certain amount of drive cycles before the ECU cottons on to the fact the fault is still there, you may well find that a relearn on the pressure sensor cures it but either way it will buy you time to decide what you want to do.

Steve.

Hi so I have the egr filter out going to let it soak in degreaser overnight, also getting vcds. Kinda off topic but I was researching things and came across some things saying you should do a timing belt maintenance around 100-120k miles. I bought mine with 97k and have 124k now and have not done anything with the timing is that something I should get done asap? 

17 hours ago, Tpowlowski28 said:

Hi so I have the egr filter out going to let it soak in degreaser overnight, also getting vcds. Kinda off topic but I was researching things and came across some things saying you should do a timing belt maintenance around 100-120k miles. I bought mine with 97k and have 124k now and have not done anything with the timing is that something I should get done asap? 

Hi I would use something like Wynns off car DPF cleaner and when finished back flush it with a jet wash on LOW power paying extra attention to flushing to the reverse way to the gas flow as you get more crud out of the way, take all the sensors out before you do anything as the cleaner often sends the sensors blind permanently.

With regard to the cam belt do it now as you could well be living on borrowed time, replace the lot idler pulleys and water pump.

Steve.