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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKVI-A6 Jetta Sedan (~ 2011+)

VW MKVI-A6 Jetta Sedan (~ 2011+) Discussions area for the MkVI (2011+) Jetta sedan. This model was originally codenamed NCS (New Compact Sedan).

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Old December 30th, 2016, 11:03   #16
n1das
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The P0401 code is for "EGR malfunction - insufficient flow". The LP EGR path has a filter in the path from exhaust back to the intake and this eventually gets clogged up from soot getting past the (cracked) DPF and restricts flow.

The LP EGR circuit takes exhaust downstream from the DPF so that it's clean exhaust being recirculated. The filter (listed as a TUBE) cleans up anything left over in the exhaust before injecting the flow into the intake path upstream of the intercooler. Note that this is different from the HP EGR path which usually takes exhaust from the exhaust manifold ahead of the turbo and injects into the intake path downstream from the intercooler.



With a cracked DPF you have some soot getting past the DPF and it slowly clogs up the EGR filter ("TUBE") in the LP EGR path. Flow in the LP EGR path eventually gets restricted enough to trigger the P0401 code for insufficient flow.

The only issue I see with driving with a cracked DPF and P0401 code is you will have the P0401 code continuously and some soot in the exhaust pipes. Given the issues with EGR and the dreaded intake clogging particularly with older TDIs, the filter clogging up effectively reduces the amount of LP EGR, equivalent to blocking off the LP EGR. It doesn't affect the HP EGR path at all. If your state doesn't require the car to pass an OBD-II scan for state inspection and you don't mind a perpetual P0401 code then you are good to go. If your state requires passing an OBD-II scan then you'll have to fix it somehow.

I had a cracked DPF and P0401 code in my 2010 JSW TDI back in 2012, starting around 70k miles. At the time I didn't know the DPF was cracked and replaced just the LP EGR filter ("TUBE") since I knew the DPF wasn't clogged up and power and MPGs were all normal. That cleared the P0401 code long enough for me to get thru an OBD-II scan to pass NH state inspection. The P0401 code came back about a week later as the new filter was getting clogged up. I drove it that way until I sold the car in 2013 at only 102k miles.

Fear not, if you don't have to pass an OBD-II scan in your state then you can safely continue driving with a P0401 code.

Good luck.
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Last edited by n1das; December 30th, 2016 at 15:48.
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Old December 30th, 2016, 12:16   #17
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one more note is that if you drive with the MIL lit, you want to check once in a while to see if there are additional codes that could be more of an immediate issue.
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Old December 30th, 2016, 15:10   #18
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I have driven mine with a cracked DPF now for about 15K miles. Drives and acts entirely normal, just soot in the tailpipe.
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Old January 3rd, 2017, 10:21   #19
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I do check for additional codes once in a while. So far, so good, so I'll bypass any repairs and drive on, just as I have been.

Thanks for the info.
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Old January 20th, 2017, 10:02   #20
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Now, it turns out, I do NOT have a cracked DPF. I just had my timing belt done and my guru said that is not the problem. Says a regen and driving it hard for 1/2 hour will clear my error code.
So the dealer performed their diagnosis for $275 and recommended a $2400 repair to the DPF and EGR for something that was not the problem. hmmmm. Almost fraudulent.
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Old January 23rd, 2017, 12:15   #21
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My CEL has been off and on now for a month or so... Seems to come on as the weather gets warmer. but it turned off today oddly, and it's over 40.
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Old January 23rd, 2017, 14:25   #22
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perhaps the borderline P0401 error is related to the winter/summer fuel, vs weather.

(probably some of each.)


Edit: I caught a couple new P0401 errors yesterday. same fuel, warmer weather.
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Old May 11th, 2017, 09:43   #23
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I have a similar issue on my 2011 Golf TDI (almost 90K mi, no mods).
I've had P0401 pop up intermittently the past few months and getting more frequent. Also most of the time more recently I have a very rough idle, cold but also after warming up. occasionally there is no rough idle at all. In the colder months sometimes I could barely get it started, and similar rough idle thereafter. There is still full power when accelerating. There is some soot in the tailpipe but I only now started looking.

I'm wondering if I could possibly damage things to the point where I can't eventually take it to the buyback appointment. I want to hold onto it for awhile first!
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Old May 14th, 2017, 07:31   #24
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Hard starting might be "frozen intercooler". You haven't given us a location or the temps it happens at, so we can only guess, but do a search and see if it matches.
I don't think dpf or egr filter issues cause rough idle, so that might be something completely different.

As long as it moves under it's own power, and isn't limping along, you should not have issues with the turn-in. If it breaks beyond that you will be screwed.
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Old May 16th, 2017, 08:05   #25
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So I want to take it on a 1000 mile road trip soon, but I still have the occasional rough idle and code on and off. Even if it is a cracked DPF, can I do so much damage that it won't run (clog up?) after a long trip?

The hard starts were mostly early spring here (Cleveland) about 40F. Has done it recently above 50F but not much now.
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Old May 16th, 2017, 09:03   #26
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I have been driving with cracked dpf for a while now. To get the MIL light off, I removed the filter media in the low pressure egr filter [you need to take it to an exhaust shop to get it cut to remove filter and weld it back] and since then the car is driving with no issues, no MIL light just sooty exhaust pipe, which I couldn't care less about it.
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Old May 16th, 2017, 09:08   #27
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Quote:
Originally Posted by tdi54 View Post
I have been driving with cracked dpf for a while now. To get the MIL light off, I removed the filter media in the low pressure egr filter [you need to take it to an exhaust shop to get it cut to remove filter and weld it back] and since then the car is driving with no issues, no MIL light just sooty exhaust pipe, which I couldn't care less about it.
Not worried about soot going into engine?
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Old May 17th, 2017, 04:05   #28
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The engine already gets some soot from the high pressure EGR loop.

the problem with gutting the low pressure EGR is more in the intake side of the turbo (my guess) which is designed to only see well-filtered air. (and the screened and cooled low pressure EGR exhaust gasses)
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Old May 17th, 2017, 10:50   #29
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the problem with gutting the low pressure EGR is more in the intake side of the turbo (my guess) which is designed to only see well-filtered air. (and the screened and cooled low pressure EGR exhaust gasses)

I think the gases are still cooled but you might be right on the intake side of the turbo, at this point I am not sure if there will be long term damage.
I have put over 10K with this set up and have not seen any performance or fuel economy issues. I guess time will tell.
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Old May 17th, 2017, 14:50   #30
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Agreed.

the VW folks put the screen/filter there for some reason.

(I have on theory that it is really there to detect a failed DPF. and that improvement in this capability is why a new LP EGR filter is part of the "fix" as described in the court docs... to do a better job of detecting failed DPFs. I have a further wild ass guess that discussion on who covers which part for how long is being discussed, and delaying approval of the "fix")
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