P0401 Insufficient EGR Flow

Hi all,

My modified 2003 Golf has been throwing the P0401 'EGR : Insufficient flow' code for a couple of months now. I've been through the previous thread for this several times but I'm starting to hit my confusion/frustration limit so I thought I'd start a new one:
http://forums.tdiclub.com/showthread.php?t=227462&highlight=16785

Here's the setup:
178k miles
Upsolute 2 chip with PP520 injectors - on there a long time, no problems
OMI from Kerma - most recent update, but didn't throw the code until a couple of months after I installed it. This necessitated the removal of the sensor that normally plugs into the CCV return, currently hanging loose.
EGR mod done with VCDS (which I own)

Here's what I've tried so far:
- Cleaned the MAF with MAF spray cleaner (although turbo seems to work fine)
- Checked EGR diaphragm with Mityvac - it does move the lever when vac is applied.
- Cleaned EGR tube with coat hanger and compressed air, cleaned out gunk in EGR part of intake.
- Checked intake manifold: Buildup is not bad, approx 1/8 inch? So I didn't clean it.
- Replaced N18 valve

My current Group 003 log from a full throttle run is below.

What's next?

Thanks.

Time Engine Speed Air Mass Spec Air Mass Actual EGR Solenoid
0.01 903 290 445 84.5
0.35 903 290 475 84.5
0.68 903 290 475 84.5
1 1029 380 465 84.1
1.35 1008 480 475 77.3
1.66 1113 515 485 66.1
1.97 1071 570 525 64.5
2.32 966 720 490 4.8
2.65 1344 560 495 19.9
2.98 1680 525 530 23.9
3.33 2037 495 625 35.9
3.65 2352 475 760 69.7
3.98 2625 490 820 84.5
4.32 2961 650 885 83.3
4.63 3360 665 970 4.8
4.98 3780 850 810 4.8
5.31 3948 850 670 4.8
5.61 3423 325 490 4.8
5.96 2478 720 620 19.9
6.28 2709 775 750 4.8
6.59 2919 820 1050 4.8
6.95 3192 825 990 4.8
7.26 3465 830 945 4.8
7.58 3696 850 920 4.8
7.93 3948 850 905 4.8
8.26 4200 850 865 4.8
8.59 4389 850 855 4.8
8.93 4599 850 830 4.8

At 900 RPM range your specified and actual air mass numbers are off actually their off through the whole RPM range, the specified and actual should be closer. What was your EGR mod? I'm assuming VCDS off road setting. In most cases your code indicates the manifold needs cleaned could be a deep restriction inside the intake. Is your MAF any good? Those specfied and actual air mass numbers seem pretty off wich would indicate a bad MAF. Your EGR duty cycle looks odd too. I'd try cleaning your intake manifold the right way. This involves removing and really getting the soot out. Don't poke wires down the manifold or try to scrap it out that soot and coking can catch in a valve seat and bend a valve stem and ruin your whole day. Good luck.

Yes, the EGR mode was the VCDS off road setting. Also, IQ is set to ~3.7 mg/stroke, if that makes a difference.
I checked my records and it has been 26k since the last time I removed and cleaned the manifold, the front of the intake didn't look as bad as I've seen it in the past, but maybe it is time to do the full pull and clean again. I didn't remember it being that long, wishful thinking I guess.
I also have a new MAF sitting around, I suppose I could drop that in just to try it. I haven't had any of the power loss problems in mid acceleration that I usually associate with a failed MAF, though.

jajohn said:

Yes, the EGR mode was the VCDS off road setting. Also, IQ is set to ~3.7 mg/stroke, if that makes a difference.
I checked my records and it has been 26k since the last time I removed and cleaned the manifold, the front of the intake didn't look as bad as I've seen it in the past, but maybe it is time to do the full pull and clean again. I didn't remember it being that long, wishful thinking I guess.
I also have a new MAF sitting around, I suppose I could drop that in just to try it. I haven't had any of the power loss problems in mid acceleration that I usually associate with a failed MAF, though.

Click to expand...

It seems to me your manifold shouldn't need cleaned at 26,000. Those MAF numbers are diffently off as far as specified and actual. From what I know that indicates a bad MAF. Seems to me an airflow restriction, like the manifold being partially blocked. In most cases a po 401 indicates the manifold or egr valve needs cleaning. In most cases the manifold. This is all I know regarding the po 401, I've had it and cleared it by cleaning my manifold. I had a half inche air hole left in mine, it was bad.

Yeah, I've seen some bad ones before, that's why I didn't think of my (relatively) cleaner one as a likely culprit, but there may be something down in the bends I can't see.
I'll probably try the MAF replacement first since I already have one and it's easy to do. If it doesn't fix the error I can do another logging run with it and at least see if the numbers change.

It's got to be an airflow restriction some where. That could be causing the MAF discripensies. I suppose you will have to fiddle around with it. It's not a major problem. Is your EGR clean inside, I'd remove it and clean it. Then look down the manifold. I know in some cases they can get sooted up in the bends pretty deep. The MAF is registering the air differences so those specifieds and actuals are the reason the ECU is throwing the code. Good luck.

Update: I replaced the MAF, group 3 logging shows the requested vs actual tracking more closely (although difference at idle is about the same as before). However, the code came back anyway. Looks like I need to find time in my schedule for a manifold cleaning. I'm not terribly concerned because the car runs fine, it's just annoying.

Glad you tracked the problem. I know mine was always the manifold and EGR sooted up. I cleaned mine last year and did the VCDS off road setting.

Well, I finally found the time for a full up intake manifold cleaning, and cleaned the EGR and cooler while I was at it. With the exception of the intercooler which I haven't touched, the intake is probably as clean as it's been since I owned the car.
Aaaaaannnddd....
It didn't fix the problem. Cleared the code and it came right back two days later.
At this point it has to be related to the OMI, although the only way for me to say that positively would be to put the stock intake back on, which I'll probably try at some point.
Either
1. The fact that this OMI (KermaTDI version) fits very tightly against the EGR diaphragm to the point that the bulb is wearing a hole in the OMI insulating cover is keeping the EGR from operating properly, or
2. The computer just doesn't know how to interpret the extra intake air properly and is throwing bogus codes.
I'm going to ask Kerma if he's gotten around to reworking his OMI to make it fit properly yet, but in the meantime next time I'm in the mood to spend a few more hours working on my car I'll drop in the stock intake to try to remove all doubt as to the cause. It's a shame, because other than the persistent code the car runs great, the OMI has reduced the smoke to its lowest level in years.