Intermittent EGR P0401 Fault

Hello Guys,



First post here. I need some help with an EGR fault that I am seeing, if I keep the car at ~1900 revs, the engine workshop light comes on and an OBD scan shows it to be the P0401 insufficient EGR air flow fault. The vehicle drives fine, what is weird is sometimes it actually goes away!



Originally when I got the error, the car started limping really bad (egr stuck open?), i took it to a local reputable garage who checked it with VCDS and said it was the EGR valve + new glow plugs. He did a delete for me (I believe he just blocked the vaccumm line). I wasn't happy with the CEL appearing and felt the cars boost was being limited. I had to go into work during the week but a family member took the car to another local garage to get the EGR changed. The garage fitted a new EGR (delphi brand) and the car drives absolutely fine except for the fault appearing!


I have one of the later 1.9tdi engines with a DPF, it is a bluemotion BLS engine, 2008 model (58 plate). The EGR is different to the other 1.9tdi engines, i believe it is electric.


Going back to the problem, I have managed to repeat the problem by keeping the revs around ~1900-~2000 for a few seconds before the fault apears again, clearing it just results in it re-appearing whilst driving when the rev range is between the aforementioned.


Any thoughts and suggestions guys will be helpful. I do believe the EGR is opening and closing; When i run Torque pro and read some information through the OBD port, the emissions tests do pass but fail when the fault appears. I have even monitored the MAF and can't see any spikes or anything to indicate something wrong there.



my current thought chain at the moment is:

- during original EGR delete or the fitting of the new EGR (delphi make) one of the vaccum lines has been damaged.
- Really clogged up intake
- Faulty EGR which is not responding correctly to the demand from the EGR
- Faulty Solenoid (anyone know where this is located?)
- Fault cooler flap (again anyone know where this is located?)
- ECU requires to re-learn the EGR --> Ross Tech's website says you cannot perform this on the PD engines, but i I beleive you can on the later model as the EGR is electric.


Since this is the later engine, the EGR system is slightly different and finding any information on this partciular model is a nightmare, everything refers to the other engine models.


I don't want to return the maybe fault EGR just to have my warranty claim rejected with them claiming that it is working fine. Also, I want to keep the car straight and want to avoid any software re-maps etc to delete the EGR+DPF (I wouldn't mind the extra BHP though!).


Any help guys? An EGR diagram for this engine would be particularly useful Also the 'normal' reading from the MAF at idle and the reading it expects during light load would also be helpful. From my research, the EGR recirculates 15% of gases under light acceleration, does anyone know the actual rev range the EGR should operate?

More Diagnostics

Okay I found this video of the BRM engine which is similar to the BLS engine, in this video the user tests the EGR valve and re-fits it: https://www.youtube.com/watch?v=DBZ6hTYYFO8


I'm starting to think the EGR valve is not opening at all and the tests that do pass are because the EGR is expected to be closed at higher revs.:


Example of a test 'pass' https://imgur.com/a/XB0ZGP6

Example of a test 'failure': https://imgur.com/a/FLkhwIR

A read out of VCDS (whilst revving): https://imgur.com/a/Qx3VGF0

The actual dreaded fault: https://imgur.com/a/o7i5xJl

I'm going to start looking at unplugging the EGR tomorrow, if the behaviour is the same as before then I can be pretty sure the valve is not operating at all.

After that I think I will have to start taking the wiring out and making sure there is nothing clogged, i still suspect something has been wired incorrectly

closer to the solution

I monitired the maf at revs 1600 and 1900 (two reference points whilst engine was hot), and then disconnected the egr. I got a circuit A high dtc fault which i expected.


The maf flow was the same as when it was plugged in, i dont think it is opening! From memory, i was seeing 32g/s at 1900 revs when the ecu expects something below 29g/s.



Im going to check the wires with a multimeter (need to learn how to use!) In order to make sure the wiring is okay. After that, I'm going to change the egr valve.



I actually have a second one, i might try plugging it into the port and make sure it opens before installing it.

more woes

I fitted another new egr valve, still get the same issue.



The manifold was dirty, but definitely not clogged.



A friend mentioned that because the fault apoears on sustained constant revs, i have a leak somewhere which would make sense. He advised me my pipe connecting to the turbo probably has a small leak in it (it looks like its in a worn out shape too).


Guys, any help? What are the chances it is leak? and what is the best way to check for a leak?

Source of Problem Found

I managed to get hold of a vw workshop manual that has some very nice diagrams for all the 1.9tdi variants. It helped massively. That and vcds, i managed to find out there is no boost leak and my egr valve is fine.


It rurns out the flap on my egr cooler isn't operating, does any one know how the flap is controlled? Is it electric or vaccum operated? Im going to get under the car next week, i don't think it is leading gases.


Does anyone know the best way to test the egr cooler?

The flap does not actually need to work, as the EGR valve itself regulates the EGR volume. It should be unsurprising that when an EGR delete is performed, the feedback to the ECU complains of insufficient EGR. There is no sensor that directly measures EGR, rather, the value is calculated by the ECU based on the MAF reading and the sensors including pressures and temperatures of the air, water and oil

When you had the EGR delete performed, did you have the vehicle tuned? Malone tuning has an excellent tune that can be loaded using MPPS. I deleted my EGR, Cooler and ASV about 5000 miles ago and have not experienced any of the issues you mention. 06 Jetta TDi BRM.


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sptsailing said:

The flap does not actually need to work, as the EGR valve itself regulates the EGR volume. It should be unsurprising that when an EGR delete is performed, the feedback to the ECU complains of insufficient EGR. There is no sensor that directly measures EGR, rather, the value is calculated by the ECU based on the MAF reading and the sensors including pressures and temperatures of the air, water and oil

Click to expand...

Hi sptsailing, the egr valve itself opens, the egr cooler though seems to be the issue. The actuator for the flap in the cooler is stuck. Is it a vaccum line that controls the cooler flap? I took the car back to the garage which did the delete and they said they did not touch the cooler, since then i have put a new egr valve in.



Here is a vid with someone who had a leak at the actuator: https://youtu.be/-25vD9tLfo0


Im going to get under the car on the weekend to confim and play around, i have a feeling whatever controls the flap is causing the issue.

Satsonic said:

When you had the EGR delete performed, did you have the vehicle tuned? Malone tuning has an excellent tune that can be loaded using MPPS. I deleted my EGR, Cooler and ASV about 5000 miles ago and have not experienced any of the issues you mention. 06 Jetta TDi BRM.


Sent from my iPhone using Tapatalk

Click to expand...

Hi satsonic, no i didn't the delete was meant ti be temporary whilst i got a new valve.



I have a dpf on my car too, its the later 1.9tdi variants that came with a dpf and i am trying to keep the car straight. Removing the egr causes issues with the dpf too from what I've heard.

The video of the leak tells another story. In my car, that bushing leak reduced the required boost and messed up drivability. Also, the EGR 0401 code indicates a flow problem. On my car the EGR valve was stuck slightly open, then it actuated more and then less open upon ecu command. Your EGR valve must shut and open on command.
So the solution to my problems of MAF codes, EGR codes, bad shifting, and stalling upon start was: Replace EGR valve and Remove the cooler, and have the shaft permanently welded in the closed position. (all Exhaust goes through the cooler, not through the bypass. I had a Frank06 cooler replacement. Now my car runs perfectly, no codes, smooth as silk drivability.

dzl_nator said:

The video of the leak tells another story. In my car, that bushing leak reduced the required boost and messed up drivability. Also, the EGR 0401 code indicates a flow problem. On my car the EGR valve was stuck slightly open, then it actuated more and then less open upon ecu command. Your EGR valve must shut and open on command.
So the solution to my problems of MAF codes, EGR codes, bad shifting, and stalling upon start was: Replace EGR valve and Remove the cooler, and have the shaft permanently welded in the closed position. (all Exhaust goes through the cooler, not through the bypass. I had a Frank06 cooler replacement. Now my car runs perfectly, no codes, smooth as silk drivability.

Click to expand...

Thanks for the reply dzl_nator. Seems like having it welded open (i might try something clever with cable ties before anything permanent) is a viable option, what i dont understand is the whole function of the bypass valve on the cooler and its purpose.


I guess the ecu commands it to open when the egr valve is also commanded to open, but what is that it is bypassing? My understanding is all the exhaust gas flow should go through the cooler (to be cooled) and go into manifold thereafter. Does the bypass valve closing simply just stop gases reaching the manifold or does it allow gases to directly reach the manifold without cooling.



If its the prior, then permanently welded open sounds like a reasonable fix but why is there this extra control? Is it just redundancy as too much gases or hot gases are bad for the engine?

The EGR cooler flap is operated by vacuum. The ECU causes the flap to move in the bypass position so that no exhaust goes by the cooler. It all goes directly into the intake manifold. The purpose of this is to help the car warm up quicker. By warming up quicker, emissions is reduced.
On my car, the warmup time increase is definitely noticed during cold weather. But in warm weather it is not noticed so much.
In my case, the seal was blown out, and I had a boost leak. This was especially noticed at low boost conditions. And I believe that at idle the EGR valve is to be closed. (please confirm) This leak reduced the Manifold Absolute Pressure (MAP) value to below required. So the fueling seemed off. It messed with the MAF, because the EGR quantity was off. So after a long diagnostic journey, I installed a Frank06 repaired cooler, put a new EGR valve(mine was not closing all the way/ and O2 sensor on, and pulled apart all the wiring to inspect for broken conductors. Car runs great now.

Tdi_car_rider: I just noticed you are in the UK and have a newer car than my 06 BRM. My BRM is more closely aligned with a BXE in Europe.(BRM= electrically operated anti shudder valve, and EGR valve) The cooler you have may be much different than the ones on the BRM motors here.

There is an Englishman at vagecumap1@gmail.com. I think his information is very good. I actually bought access to the full site from him. It will help you get up to speed really quick on diesel control.

Correction: US BRM engines more closely look like a BLS and BXJ engines in Europe, but without a Particle Filter.

part ordered

Yh that's what i understand too based on all the pictures I've seen of the brm engine, the egr cooler is different though.

I think the US has had stricter nox emission rules hence why the brm engine has the cooler, in the UK only later vw engines have a cooler.

I was under the car over the weekend, its really awkward getting at the cooler with axle stands and a jack! I've ordered a new cooler and will get the garage to fit it.

Interestingly enough the part i ordered: https://www.ebay.co.uk/itm/EGR-Valv...a-Octavia-1-9-2-0-TDI-03G131512AD/18358358127

The part number has a suffixed 'D', it supersedes the original part. I think its a tacit acknowledgement from vw that the cooler design is flawed.

An oem cooler was costing almost three times as much! Has anyone had experience with ebay and possibly made in china parts? What worries me is the cooler is connected to the oil and coolant lines, i think the vaccum line joins onto the brakes too!

How much should a garage charge? Ive had an £80 quote all the way through to a £150 quote, apparently there is alot of parts inbetween that need to be disassembled in order to get at the cooler.

A final update to close this thread, I had the cooler changed, it was blocked so bad that the the valve was not opening which re-directed the gases through the cooler.


It's a long job too... took the garage 2-3 hours to do.



Lessons learnt: If the egr valve is working then its most likely the cooler or a leak somewhere there.