PO40100 (EGR flow insufficient) CXGB

[Wills640]

Hi All,
I have a 2017 T6, CXGB engine, 47000 miles, had a new egr and cooler at 36000 miles. (genuine VW) Light came back on recently with the above code. Fitted another Pierburg EGR valve, same fault, Replaced cooler pipe with modified slotted pipe and still same fault. Any suggestions. Light stays out for a few miles when reset. Thanks.

 

[Howzat]

Your engine may be dumping too much crap into the exhaust system. Does it also regenerate a lot? Say every 50-100 miles or so?

 

[Wills640]

Your engine may be dumping too much crap into the exhaust system. Does it also regenerate a lot? Say every 50-100 miles or so?

Thanks for the reply.
Uses no oil. DPF completely clean. No ash content on diag. Egr valve removed was relatively clean however front Egr pipe had a build up of carbon although far from blocked. Rear was clean.

 

[manfrotto]

You are the second one to report this error in tha last few days....

Post in thread 'Another P0401 EGR fault'

22 Oct 2025

I’ve only owned the van since march but I’ve just had a look back on some of the paperwork I got with it and the egr valve and pipe was replaced sept last year… surely it can’t be that as from what I’ve read should be good for 50000 miles or 10 years, unless it potentially wasnt done properly which I find hard to believe as the work was done at a pretty high end garage in our area

I don't know where you get those numbers from?

Mine has been flushed twice, and the code has now come up a third time. 42k and 6 years.

• CAB

Might need to start a poll?

 

[Micktheplasterer]

You are the second one to report this error in tha last few days....

Post in thread 'Another P0401 EGR fault'

22 Oct 2025

I’ve only owned the van since march but I’ve just had a look back on some of the paperwork I got with it and the egr valve and pipe was replaced sept last year… surely it can’t be that as from what I’ve read should be good for 50000 miles or 10 years, unless it potentially wasnt done properly which I find hard to believe as the work was done at a pretty high end garage in our area

I don't know where you get those numbers from?

Mine has been flushed twice, and the code has now come up a third time. 42k and 6 years.

• CAB

Might need to start a poll?

I’ve got it on my crafter, had new egr fit last week. Still firing codes up. I’ve got a new one today P0402 twinned with the 401

 

[Wills640]

Quick update.
Replaced rear egr flexi pipe with modified part. showed no signs of carbon build up or leakage. reset code and after a few hundred miles no fault code.
I can only assume it has a better flow on the modified pipes and combined with the front pipe increased flow to satisfy the sensor.

 

[Robert]

Photo, part number please?

 

[T6paulw]

Hi. Bear with me as a new member with no past experience of posting on Forums!

Just picked up a used 2017 T6 with the 102 engine, 129k miles. Felt the best evaluation would be a decent run, mainly motorway. 130 miles in, EML illuminated. Although I have a reasonable mid range Launch FCR, I just had my OBD 11 with me. I found a number of codes on the van when I picked it up, deleted them, but the significant ones that returned are;

EGR P040100 EGL Low flow and.....

Reductant System Performance P204F00

(from my ODB11 that I had with me at the time.)

The van has 129k miles on. It has a good service history, had the first EGR and cooler at around 80kmls the another at 108kmls. That means the one presently fitted has done only approx 20k. The MOTs show its done more then 1000 miles per month immediately before purchase and generally throughout its life miles that will have been mainly 'motorway'.

I have reasonable mechanical knowledge, ability and experience with VWs in general, but not with AdBlue systems.

My concern is that although I assume we will need the EGR replacing, is there a cause and effect between the likely EGR failure and the high NOx reading, or are we potentially looking at two separate issues?

The car dealer (NotVW) says that they will look at the problem. My concern is that they will just try additives or an EGR clean, when a replacement EGR seems to be the only longer term solution from what I read here. Has anyone had success with any cleaning!

In terms of how it runs at the moment; it is sometimes a bit hesitant starting from cold and that's about all. The initial idling can be a bit lumpy, but soon settles. On a steady motorway run in busy traffic, it hits 45 to 50mpg and pulls well. No sign of blow by. Too early to comment on oil consumption. Coolant level steady after 200 miles. It did a REGEN on the day of collection and I wasn't sure if it began a second one even after a long run, which makes me suspicious that it's looking at more frequent regions than I see as normal, compared with other diesel cars I have.

I read on the forum of past VW software updates in relation to this issue and I wouldn't know if that has been done from the history I have.

Any general advice from similarly afflicted members would be appreciated to help me find a way forward. It seems an all too common T6 problem!

Many thanks

 

[EG-argh]

Hi. Bear with me as a new member with no past experience of posting on Forums!

Just picked up a used 2017 T6 with the 102 engine, 129k miles. Felt the best evaluation would be a decent run, mainly motorway. 130 miles in, EML illuminated. Although I have a reasonable mid range Launch FCR, I just had my OBD 11 with me. I found a number of codes on the van when I picked it up, deleted them, but the significant ones that returned are;

EGR P040100 EGL Low flow and.....

Reductant System Performance P204F00

(from my ODB11 that I had with me at the time.)

The van has 129k miles on. It has a good service history, had the first EGR and cooler at around 80kmls the another at 108kmls. That means the one presently fitted has done only approx 20k. The MOTs show its done more then 1000 miles per month immediately before purchase and generally throughout its life miles that will have been mainly 'motorway'.

I have reasonable mechanical knowledge, ability and experience with VWs in general, but not with AdBlue systems.

My concern is that although I assume we will need the EGR replacing, is there a cause and effect between the likely EGR failure and the high NOx reading, or are we potentially looking at two separate issues?

The car dealer (NotVW) says that they will look at the problem. My concern is that they will just try additives or an EGR clean, when a replacement EGR seems to be the only longer term solution from what I read here. Has anyone had success with any cleaning!

In terms of how it runs at the moment; it is sometimes a bit hesitant starting from cold and that's about all. The initial idling can be a bit lumpy, but soon settles. On a steady motorway run in busy traffic, it hits 45 to 50mpg and pulls well. No sign of blow by. Too early to comment on oil consumption. Coolant level steady after 200 miles. It did a REGEN on the day of collection and I wasn't sure if it began a second one even after a long run, which makes me suspicious that it's looking at more frequent regions than I see as normal, compared with other diesel cars I have.

I read on the forum of past VW software updates in relation to this issue and I wouldn't know if that has been done from the history I have.

Any general advice from similarly afflicted members would be appreciated to help me find a way forward. It seems an all too common T6 problem!

Many thanks

Hello, did you have any luck getting to the bottom of this? My ex vw fleet T6 2019 with 173k miles is also on its third EGR and after 10k miles with the latest EGR has just started again with the same P0401, P204F / P20EE with the bonus of P164E - oil pressure regulation valve. Seems mad to need a new EGR again! Had the software updated last year, too.

I do a mix with some Devon lanes but mostly motorway - at least 2x 1hour or 2 x 2hour motorway drives per week. Have got through about 1L of oil over the past 10k miles. No drop in coolant. Drives well, though suspect the turbo might be slightly sticky at times, hard to tell. I get at least 50mpg on the motorway (managed 60 mpg once on a 2hr drive!), so no other complaints. £1200 each year for a new EGR seems silly though.

 

[T6paulw]

Hi. In the end, we had two problems. The NOX sensor was replaced….and it would only work with a genuine VW sensor, which was very expensive and on back order for six weeks! A vw software update was also advised in relation to the egr codes.
The egr codes need to be looked at by VW to determine what the cause of the code may be. VWCV have a process to clean egr valves in some instances.
The egr low flow resolved with Wynnes fuel system cleaner and possibly the update.
I now run with permanent Archoil diesel additives…. Effectively making standard diesel into premium diesel.
Look at only using good quality fuel too.
I found one of the intercooler hoses was loose. That could have been the cause of the code in my case.
If your engine is burning oil, that would also soot up the egr.
Good luck and sorry I can’t specify a solution for this!