Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

pcdreams · May 11, 2018

For us newbies, I'm wondering if there is a key to that Image you posted of the vacuum lines. I'm sure N75 and other numbers mean a lot if you know what you're doing, but they're a bit confusing to us newbies without a reference.

Thanks,

Don

UPDATE: Answering my own question. Here's a link to the full diagram https://www.google.com/search?q=m26...UIDCgD&biw=1600&bih=794#imgrc=dHwf4mH2TIZH7M:

BobnOH · May 11, 2018

http://forums.tdiclub.com/showthread.php?t=290286
or
https://farm9.staticflickr.com/8722/16872254906_166acf578c_b.jpg

watchingcrow · Jun 27, 2018

overboost 0234 woes

I have replaced the N75, Air Filter, Actuator, most of the Vacuum Tubes (some look new) the way the Limp Mode occurs has changed but not gone away. And no engine warning light. I drove to 2.5 hours to Santa Cruz from S.F. and by keeping the Tach under 30K no problem, but if i accelerate going up the hill, which happened once, i lose turbo, but not all power, I am still able to mosey up the hill and on the way down put in neutral and ignition off and on and i am good to go. But, coming home, in normal street mode, suddenly i went limp and also got the orange engine light and now the 0234.

The turbo is only 5 years old as i blew it up driving over the Grape Vine, on the way to LA, all smoke and no power crawled into LA and to a Dealer, $1500 and 4 days later i had a new Turbo,but they left some of the old Vacuum lines for some odd reason.

What oh what am i to do?

Am Retired and as they say On A Fixed Income, and am willing to struggle with doing some of the work myself.

Help

Michael Patrick McAnelly
San Francisco

alphaseinor · Jun 28, 2018

Did you check the vacuum actuator on the turbo to see if it moves the full 1/2" or so, and does so smoothly?

What is your code? do you know if it's underboost or overboost?

Bosserdet · Jun 29, 2018

Yes, the actuator can be the problem. I just pulled out the turbo in my BHW (2005 Passat TDI Wagon B5.5) and that was the first thing I noticed was the actuator was not moving. That was because of all the crap that was inside the turbo. During the discovery process I found some broken pieces of metal from a couple of the veins.

I trashed it and installed a new one. No more codes and no more limp mode. I am thinking that the veins were stuck in a position that let me drive it around as long as I did not try to put any real load on the engine. Seems like every time I was trying to accelerate hard or going up a hill it would find limp mode. Sometimes it gave me a code and some times not. The code would be overboost.

Runs fine now.

watchingcrow · Jun 30, 2018

alphaseinor said:
Did you check the vacuum actuator on the turbo to see if it moves the full 1/2" or so, and does so smoothly?

What is your code? do you know if it's underboost or overboost?

Hi Alphaseinor;5419805,
Sorry for the delay.
I am getting p0234 Overboost.

I replaced the Actuator but did not test it, thought replacing did not require a test.
What is that Vacuum Test device i see on some of the videos?

Like i said it is a relatively new Turbo (if the dealer actually replaced it) and I really don't drive much, and that could be part of the trouble, ie not enough high speed, mostly city 35mph.

I am confused if maybe there is another thing to replace. I replaced n75 and the "actuator" but is there another thing - i watched a video and a wastegate was mentioned and when i checked one of the Vacuum Tubes that connected to something under the engine it looked similar to other parts.
It would be tough to replace and then there is the MAP, which i have heard really does not fail and it is also hard to get at. I think you have to remove the grill and headlights.
OH, i did not replace the MAF, I cleaned it and replaced the airfilter. Maybe that is the bugger???

Thanks.
Michael Patrick

alphaseinor · Jun 30, 2018

I'd stop throwing parts at it. Almost everything you listed didn't fix it, so why would replacing more help?

The actuator, you just need a hand vacuum pump, lay under the car, at the back of the engine, on the turbo, there is a vacuum line, connect the pump, and see if it moves (should start moving about 5"HG or less). it should move about 1/2" until it stops, and should be smooth motion.

Since you have an Overboost, how's your EGR/intake manifold look? Any clogging?

watchingcrow · Jul 2, 2018

overboost 0234 woes

alphaseinor said:
I'd stop throwing parts at it. Almost everything you listed didn't fix it, so why would replacing more help?

The actuator, you just need a hand vacuum pump, lay under the car, at the back of the engine, on the turbo, there is a vacuum line, connect the pump, and see if it moves (should start moving about 5"HG or less). it should move about 1/2" until it stops, and should be smooth motion.

Since you have an Overboost, how's your EGR/intake manifold look? Any clogging?

No clue, so i am "searching" that topic to see what i must do to inspect.
My first look shows that I must disconnect the INLET Manifold to view it.
I will get back to you once i have managed that process.
Thanks again

Michael Patrick

watchingcrow · Jul 2, 2018

Also must find a cheap hand vacuum pump, won't use often i reckon.
There are really cheap ones - plastic, and such, but fear them hahaha

alphaseinor · Jul 2, 2018

just get a mityvac

Amazon link here currently $40

watchingcrow · Jul 2, 2018

Thanks

watchingcrow · Jul 8, 2018

Intake Manifold

alphaseinor said:
I'd stop throwing parts at it. Almost everything you listed didn't fix it, so why would replacing more help?

The actuator, you just need a hand vacuum pump, lay under the car, at the back of the engine, on the turbo, there is a vacuum line, connect the pump, and see if it moves (should start moving about 5"HG or less). it should move about 1/2" until it stops, and should be smooth motion.

Since you have an Overboost, how's your EGR/intake manifold look? Any clogging?

Hey there Alphaseinor;5420400
So, I removed the hose that connects to the EGR and there is no build up what ever. The flipper moves freely, the only concern is there i a light layer of black grease on the surfaces. I took two of the bolts off that allows me to remove the EGR, but the third one is hidden and virtually inaccessible without removing more things around it. The only way i could loosen that bolt is maybe with a very small needle nose vice grip. But, before i go that far, i wonder if i need to go further, if there is no build up at all inside the EGR? Any thoughts.

Bosserdet · Jul 9, 2018

Good Point

alphaseinor said:
I'd stop throwing parts at it. Almost everything you listed didn't fix it, so why would replacing more help?

The actuator, you just need a hand vacuum pump, lay under the car, at the back of the engine, on the turbo, there is a vacuum line, connect the pump, and see if it moves (should start moving about 5"HG or less). it should move about 1/2" until it stops, and should be smooth motion.

Since you have an Overboost, how's your EGR/intake manifold look? Any clogging?

Alphaseinor has a good point. Sometimes you forget the normal things you do out of necessity. Taking the intake off the BHW or B5.5 and cleaning intake and the ports to in the head is something I do about every 50-60k.

watchingcrow · Jul 9, 2018

HI

So i understand about the Manifold.
As i said, I am struggling to get to the manifold. The EGR seems nearly impossible to remove as the third bolt is literally inaccessible, several other pieces must be removed to get to that third bolt. So, before i go to all of that trouble, and i am NOT unwilling to, i just dont want to do that if it is unnecessary, you know. I removed the hose on the front of the EGR and looked inside and though there is a sheen of black grease on the surface inside it certainly is clogged. Is that an indication that the Manifold itself is not clogged or are those two completely unrelated signs?

If there is no manifold clogging, maybe i just need to get the vacuum pump and check at that nozzle under the engine to see what i am getting. Then, lets say it is not up to snuff? What does that tell me that i do not already know. I have a p0234 code already...I am perplexed at the issues and their resolutions. BUT I AM DETERMINED to solve this. The car does not get that much use. Twice a year i drive to Santa Cruz, 100 miles, other than that 15 minute street trips to the market is all. The Turbo is only 5 years old, at less than 6k miles a year on driving.
So, what to do next ....
Thanks i really appreciate all the help. This Forum has been a big help even if nothing has worked so far LOL>

Michael Patrick:

watchingcrow · Jul 9, 2018

Also, are there two actuators? I purchased and replaced the EGR

But see often mention of the VNT Actuator, is that something else and if so, where is it located?

BobnOH · Jul 9, 2018

There are several parts called actuators. The VNT Actuator is on the turbo.

watchingcrow · Jul 9, 2018

https://www.facebook.com/photo.php?fbid=2290544667638643&set=pcb.2290544710971972&type=3&theater

View of EGR Valve condition.

alphaseinor · Jul 9, 2018

The EGR comes off, but you must remove the L pipe.

I wasn't suggesting replacing your EGR... I think you keep throwing parts at it, at this point I would just suggest finding someone to help you, since you've probably dumped a grand in parts into not fixing the car.

flee · Jul 9, 2018

You haven't said so I have to ask: did you properly adjust the turbo actuator yet?

watchingcrow · Jul 10, 2018

BobnOH said:
There are several parts called actuators. The VNT Actuator is on the turbo.

I think i found it, accessible from under the vehicle, easy to attach a Vacuum Pump, not so easy to remove. But...there you go...the plight of the amature/shade tree mechanic.
MP

watchingcrow · Jul 10, 2018

VNT Actuator

flee said:
You haven't said so I have to ask: did you properly adjust the turbo actuator yet?

I replaced the EGR Actuator and thought THAT WAS the Turbo Actuator. So, no. I am about to purchase a Vacuum Pump to test it.
Then i will try to figure out how to "adjust" it.

Thanks

Michael Patrick

watchingcrow · Jul 13, 2018

only $47 in parts so far.

alphaseinor said:
The EGR comes off, but you must remove the L pipe.
I wasn't suggesting replacing your EGR... I think you keep throwing parts at it, at this point I would just suggest finding someone to help you, since you've probably dumped a grand in parts into not fixing the car.

So far i have spent:$47 on parts and $87 on the Vacuum Pump and OBDII.
So, considering how much it would cost at the dealer...
I am ahead of the game, not to mention my education, and i discovered a loose wire and now i have my AC back, after 2 years of just not bothering, and tightened up some loose bolts on the "Pan".
But i am frustrated. The problem still exists but is not as severe as it was. So, that is really weird. How do you fix part of an on going problem. I guess there were at least two causes to the error code. Now that i have the Vacuum Pump, I will test the VNT actuator. I HOPE LIKE HELL THAT THAT IS NOT THE PROBLEM. Because it DOES look beyond my paygrade. Everything else I can do - AND i may have to just replace every bloody posible part until i find the culprit.
IF the vacuum is OK on the Actuator, where do i go next with that Vacuum Pump?
Thank you very very much
Michael Patrick

watchingcrow · Jul 13, 2018

alphaseinor said:
The EGR comes off, but you must remove the L pipe.
I wasn't suggesting replacing your EGR... I think you keep throwing parts at it, at this point I would just suggest finding someone to help you, since you've probably dumped a grand in parts into not fixing the car.

I just wondered if the EGR is pretty clean should i still try to get at the Intake Manifold. I was guessing that if the EGR is clean the Manifold should not be too messed up either.
Yes/No?

Thanks again for you time.
Oddly i cannot find anyone that does diesel around me - except my VW Dealer and, well, They might say i need a new Turbo just to make it easy and the Turbo is only 3 years old. (less than 10k miles a year for my sweet BioDiesel - ONLY - TDI.

watchingcrow · Jul 13, 2018

So, looking around at threads pertaining to 0234 and overboost etc i found one about the MAF sensor. Changing the air filter and cleaning the Sensor and the housing inside seemed to improve my situation without completely fixing it. So, maybe back to the Sensor. I read again about disconnecting and running the car without that to see if that improves the situation or it just stays the same. See that that is harmless and free and does not require me getting dirty that is my next step. If that is the problem then i spent unnecessarily on those other parts and maybe can return the $43 Vacuum Pump (unopened as yet).
I will post my progress on this. I really really do not want it to be ANYTHING to do with that VNT Actuator as I can hardly see it much less have to do that manual test or God forbid have to replace it. Who puts something seeming that important to a vehicle so out of reach??? Anyway talk to you soon.

watchingcrow · Jul 14, 2018

I must have lost the interest of the group and if i am too much of a rookie, sorry.
I am really doing all the research i can to figure out and solve the problem.
Apparently Overboost and Limp mode is a wild ride on these TDIs.
From my hours of reading the problem could really be just about anything along the line.
With that said i just read that one Boost problem was solved by going around the Vacuum Return Check Valve.
Vacuum Check Valve-ALH 046905291A
But reading what that does made me wonder about the efficacy of doing that. I mean it limits the Vacuum return to the N75. So, is that something to consider, even just to check the problem? Can that Valve be cleaned with electric cleaner? Or just canned air or what.
I guess I am going to have to open my Vacuum Pump Tester today and check the Pressure read on the Turbo Actuator. I am looking for the readings i was given by "alphaseinor" but have yet to find that post in my thread again. Anyway. This has been both painful and fun at the same time. And I have fixed other pending problems along the way so it has been very very worth it all.
Thanks to anyone who has opined for me.
Thank You ALL>

watchingcrow · Jul 14, 2018

Hand Pump

alphaseinor said:
I'd stop throwing parts at it. Almost everything you listed didn't fix it, so why would replacing more help?

The actuator, you just need a hand vacuum pump, lay under the car, at the back of the engine, on the turbo, there is a vacuum line, connect the pump, and see if it moves (should start moving about 5"HG or less). it should move about 1/2" until it stops, and should be smooth motion.

Since you have an Overboost, how's your EGR/intake manifold look? Any clogging?

Rereading your post i see you never said Actuator here. You say "on the Turbo, there is a vacuum line.
I just tested the vacuum on the Actuator with the Mityvac and it seems to be fine. It moves smoothly and gets up to about 26 on the meter and holds that as long as i let it. I am guessing that means the Actuator is not the problem.
I will look for another vacuum line coming off of the turbo itself. That said. Going backwards from the Actuator, where do i next use the Pump and this is all with the engine off, or are there times when i should try testing with the engine on.
Also, i saw a post where the member said he bypassed the Return Check Valve and found that solved his problem. If i were to do that, and that solved the problem...replace that valve or what?
Thanks sorry for bugging you.
I would be glad to reimburse you for your time with me, if that is a good thing to do. I get that you are a professional and I am an idiot/rank beginner.

Michael Patrick
San Francisco

watchingcrow · Jul 17, 2018

overboost 0234 woes

Canadian_Grizzly said:
Diagnosing and Fixing Limp mode for A4 1.9TDI
By Canadian Grizzly

Read the entire post prior to jumping to conclusions.

This is a general overview on how to diagnose and fix a A4 1.9TDI that goes into “limp” mode due to an overboost of the turbo. While I’m by no means an expert I’ve gleaned this information through information on this forum and my own experiences.

Limp mode happens when you are accelerating, often up a hill, or passing and the car suddenly seems to lose all power. Power is immediately restored when you cycle the ignition. What has happened is the computer has sensed that the turbo has created too much boost and the computer shuts it off and goes into safe mode.

There are a number of different reasons why the car may overboost… some being very simple to verify and fix and others more complex. The majority of overboosts are created by:

Bad Maf (Oxygen Sensor)
Leak in the vacuum system
Faulty N75
Bad actuator
Dirty gummed up turbo causing variable vanes to jam or stick

Some members have experienced overboost due to coked up intakes as well. This is a maintenance issue. See below for links.

If it only occurs occasionally try to find a long uphill slope on the highway and try to accelerate and reproduce limp mode. This will help later to see if the problem is resolved when you try again with similar circumstances.

Bad MAF
One of the easiest to check...but you will get a CEL (Check Engine Light). All you have to do is disconnect the MAF and give it a test drive. If power is same or improved, replace. Read this thread for one example... http://forums.tdiclub.com/showthread.php?t=215165

Vacuum Leaks
Most problems with the turbos are simple leaks in the vacuum lines. It is hard to see on the cloth covered stock hoses and if your car is past warranty it is best to simply replace all the lines. Here is a link of what you need… http://forums.tdiclub.com/showpost.php?p=1566427&postcount=30 Note to Canadians... mcmaster won't ship to us so I recommend sourcing the lines (and any other necessary parts) from Brian at Roseland http://www3.ns.sympatico.ca/roseland/VWPartsA4.htm
Be very systematic. Remove one hose, cut new one to length and replace that one hose and so on. That way you won’t screw up. When removing lines carefully work them off with a screw driver or carefully slice them with a razor and then slide off. Be especially careful if its cold. When you encounter a check valve ensure that it is also working correctly.

Also check the large vacuum line on brake booster…if you have experienced any hard brake pedal situations that will likely be the culprit. Ensure that the hose to the bottom of the airbox is plugged in as well, this one is commonly overlooked. If you haven’t replaced the hoses and think you have ruled out a leak… start checking again as this is the single most common reason for most overboost situations.

The top line on the N75, labeled 'vac' is where unregulated vacuum is drawn. Regulated vacuum is pulled through the larger 5mm ID line labeled 'out` The 5mm ID line opposite the other lines is the vent which vents the regulated line to atmospheric pressure.

Even if the N75 is good, it it doesn't have solid vacuum getting to it (top hose 'vac' ) it will not send vacuum properly out the 'out' port just below the vac port. It is also important that the vent port is clear. It's on the same side of the valve as the connector.

2 test options posted by Anut:

1. disconnect the 'vac' hose. Connect a mighty vac to the hose. Start the car. You should get >25 inHg vacuum.

2. connect a vacuum hose directly from the rigid brake booster vacuum line to the 'vac' port on the N75. You'll get an EGR code, but your turbo oughta work great.

If 1 doesn't occur, of if 2 fixes the problem; find the vacuum leak. Vacuum is drawn from the rigid line. The line splits twice such that you have 4 unregulated vac lines. One to the N18 (EGR), one to the N75 (turbo), one to the vacuum reservoir and one to the N239 (anti-shudder valve).

Faulty N75 solenoid
The N75 is the solenoid that adjusts the vanes on your turbo. On your car it will be on the firewall just to the left of the airbox. It has a grey top and some vacuum lines attached to it. If it is not working then you would be getting an overboost situation.

You can also check that the N75 is working and moving the actuator on the turbo. This is a little more difficult. Remove engine cover… use a mirror and a flashlight and watch or feel the actuator as another person puts the ignition key on. It should cycle and move properly. As in diagnosing many things on these cars a vagcom comes in very handy as you can ask the computer to cycle the N75 while you watch the actuator. With the engine running, in VAG-COM go to Group 011. Down in the lower left of that VAG-COM page is "basic settings." Click this on. You'll see the N75 go "off" and "on." Then, put a light down against the lower firewall (just in front of where the passenger's feet would be) and position a mirror so you can see the back of the turbo. As the N75 cycles, you'll see the VNT actuator rod move up and down, about 3/4" each way. If this test is ok, you can assume that the N75 is working ok.

If it doesn’t seem to work then swap the EGR solenoid, N18 (same looking part just to the left of the N75 and with black top not grey) with the N75 and try again.

Faulty Actuator
If this doesn’t solve then you either have a faulty actuator or stuck vanes in the turbo. If you can get your hands on a vacuum pump attach it to the actuator and see if it holds vacuum. If not then purchase a new actuator. Dealers normally don’t carry the actuator as a separate part as they want to sell you an entire turbo. These can be purchased by a number of vendors in the states and through Roseland in Canada.

Test the adjustment of the VNT actuator. It should start to move at 3-5 inHg, and be on the stop (fully open) at 18 inHg. Less vacuum necessary, and it will spike. More, and it takes too long to make boost, and drivability is poor.

Here is the TSB from VW on swapping and testing the actuator. http://pics.tdiclub.com/data/500/Actuator_TSB.pdf

Jason has a couple videos of a actuator in action. http://forums.tdiclub.com/showthread.php?t=330149

Sticking turbo vanes
Now failing all of the above it might be the hardest job which is cleaning the actual turbo. Note I said clean not replace. Here is the link thanks to Drivbiwire on how to accomplish this task… http://forums.tdiclub.com/showthread.php?t=140910

PLEASE NOTE: If you take it to a dealer they will diagnose a blown turbo and replace what is probably a perfectly good dirty turbo. If you are daunted by the task find a TDI Trusted Guru, look at the sticky in TDI 101 or go to a local GTG (get together) general discussed and planned the regional forum areas.

Other power sucking maintenance that should be performed.
Snowscreen cleaning… http://forums.tdiclub.com/showthread.php?p=1344400#post1344400 For Beetle http://forums.tdiclub.com/showthread.php?p=332954
Intake Manifold cleaning (just do it…really) http://pics2.tdiclub.com/gwillie/VW/Sballintake/INTAKEMAN101b.htm

Thanks to Fred
Without Fred and this forum none of this information sharing would be possible. If this thread was helpful and you saved mega bucks fixing or diagnosing the problem yourself, please consider a donation (see paypal button on home page) to ensure that this site remains available in the future.

I have not just read all of your posts and attendant documents, but have read quite a few other items on the web about this.
The one thing i have not done so far is inspect the Intake Manifold. I have looked at the EGR and it is clean but getting that third bolt off to remove the EGR looks nearly impossible. But, i will struggle on. I was just hoping it not necessary.

OH, I should add that since buying the car 10 years ago i have ONLY EVER USED BIODIESEL and only the 99% kind at Dog Patch Biodiesel in San Francisco (my home). I have heard that because of that the likelyhood of carbon build up is nearly ZERO. What do you say?

C.G. Thanks for all you do

Michael Patrick

diesel_dogg · Aug 2, 2018

Canadian_Grizzly said:
I've never heard of a difference between cruise and your foot prior to this thread....interesting.

I was using CC on a hill and after I had to shut it off, overboost.
Never noticed the issue until then.
CC would take me over the hill, while the pedal would overboost.
Now that I've replaced N75 & the vacuum lines, CC reacts as the pedal does.

The new issue is a surge, on the same hill. Near full throttle i can feel it surge no noticeable drop in rpm',s, which goes away as soon as the load is removed.
Rpms drop ~700 op

No ce light.
No surge other than under load.

Tdipower86 · Jun 12, 2019

03 golf, chasing down intermediate limp mode, my question is the nipple coming from the vacume pump wiggles a little bit is this normal. if not can I rtv around it or should I just replace the pump? thanks in advance

flee · Jun 13, 2019

It shouldn't be loose. That is often a source of vacuum leaks.
RTV or JB Weld seems to do the trick, just get it really clean.

Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

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