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

[uzi_cupra]

I changed my vacuum control module this morning -

But no luck what so ever.
Every pipe is holding pressure and vacuum except the 2 which come off for the old egr and anti-shudder valve as they are no longer in use (this was always the case and never been a problem).
Actuator holds plenty inHg vac and the rod moves down and releases fine when vacuum is released.
Fuel filter and air filter are fine and the intake is spotless.
The brakes feel fine and there is definitely no boost leaks from the turbo through to the intake - pressure tested this many times to check and they are fine.
The turbo is coming off to fit a new manifold so will bench test the actuator and ensure it is definitely not at fault.
I have disconnected the MAF sensor and this doesn’t make a difference (even though it is mapped out) and it just comes up with a fault.
I disconnected the MAP and it throws up a fault with the traction control light.
This really has been an annoyance - esp because i'm not doing the usual "newbie" thing and ask before doing the checks.
I surely can't be missing something?

 

[uzi_cupra]

2 faults are showing now:
Charge pressure control: Negative deviation
Altitude/Boost pressure sensor: Implausible correlation - this has only started to come after I put in a 4 bar MAP sensor

Gods, I hate this issue. I've been suffering from this for a couple years now and I just can't find a solution. Replaced MAF, replaced N75, replaced vacuum lines, tested turbo actuator and that's fine. I still have the damn problem.

It is so annoying!
Let us know if you find the fix.

I have been trying every single day over the past few weeks and fixed a few minor things here and there in the process but not the limp mode issue.

 

[uzi_cupra]

I think i have found the problem...my stopscrew from the turbo is missing...it must have come off over time from vibration.
I hope this is the problem. The turbo is coming off and I will set up the stopscrew and actuator on the weekend. Hopefully this will be the fix!
What do you guys think?

 

[Ruffrida]

Ya could be on the money there, whilst i was adjusting my actuator i noticed mine was no where near the arm.

Adjusted it and hay presto not had limp home for a while now.

Hope this sorts it i know how much this can get to you

 

[uzi_cupra]

After a long and groling attempt of different approaches i finally fixed my problem. Firstly let me describe this problem - i had a burst brake pipe which i changed - nothing else was changed and all was put back together however I lost boost.
This made me think it was a vac issue but after testing each hose all were fine.

I was changing my manifolds and thought this would be best time to bench test the actuator - when i tested it on the car the rod would move however only at high vacuum instead of initiating at 2-5 inHg.

Somehow my actuator rod managed to wind it self a lot longer than what it should have been which meant when it tried to draw vacuum the rod would move but not very much and it would take high vacuum to initiate movement.
I simply took it all apart and set it up as it should be, begins to move nice and early and at 18.5inHg a feeler guage of 0.05mm is locked between the stop screw and VNT lever.

Finally all sorted!
If anyone else experiences similar issues test the actuator and ensure the arm begins to move at 2-3 inHg and stops at 18inHg - this may be fine tuned depending on set up.
Thanks guys

 

[Ruffrida]

After a long and groling attempt of different approaches i finally fixed my problem. Firstly let me describe this problem - i had a burst brake pipe which i changed - nothing else was changed and all was put back together however I lost boost.
This made me think it was a vac issue but after testing each hose all were fine.

I was changing my manifolds and thought this would be best time to bench test the actuator - when i tested it on the car the rod would move however only at high vacuum instead of initiating at 2-5 inHg.

Somehow my actuator rod managed to wind it self a lot longer than what it should have been which meant when it tried to draw vacuum the rod would move but not very much and it would take high vacuum to initiate movement.
I simply took it all apart and set it up as it should be, begins to move nice and early and at 18.5inHg a feeler guage of 0.05mm is locked between the stop screw and VNT lever.

Finally all sorted!
If anyone else experiences similar issues test the actuator and ensure the arm begins to move at 2-3 inHg and stops at 18inHg - this may be fine tuned depending on set up.
Thanks guys

Really glad to hear you got it sorted bud, a bit random how the actuator had moved on its own, but knew you would get there in the end, nice 1

 

[whitedog]

A month ago you said that the rod length was fine.

 

[uzi_cupra]

A month ago you said that the rod length was fine.

I was getting boost only after 3000rpm and it slowly got worse.
The rod was moving which made me think the length would be fine as it was set up (and running 2000 miles) perfect before this encounter.
I was only able to visually check if it was moving when i had a vac pump on it...

 

[Aridzonan]

N75 Fix

I had just cleaned out my intake manifold. When I noticed a reduction in power and finally no turbo. I used your procedure and N75 was indeed the culprit. My Hayes manual gave a +25 ohm for an acceptable resistance. Mine was 17 ohms. I did manage to get the "Check Valve" in backwards. After troubleshooting that problem my turbo returned with a vengeance. Thanks mucho for the sage advice!!

 

[brianteel]

mine does not move at all with a vacuum pump and does not hold a vacuum. I guess the actuator is bad?

 

[whitedog]

mine does not move at all with a vacuum pump and does not hold a vacuum. I guess the actuator is bad?

Did you test the actuator right at the actuator nipple, or at the hose leading to it? If you tested it at the actuator, and it doesn't hold a vacuum, then, yes, your actuator is bad.

 

[rubadub]

I feel like all the information I could need is here. I am having what seems like the same issue as UZI. Up until 3k RPM I cannot build any manifold pressure. After that, it spools up like normal but then goes into limp mode at around 16 psi with the P1556. 10k miles ago I installed a VNT-17, injector nozzles, 3bar map, cleaned the manifold and a upsolute tune. I really hope that the vanes aren't sticky being that the turbo is brand new, however I put a mityvac directly to the actuator and it took around 15"Hg to move the actuator.

Could the rod being out of adjustment cause the turbo not to respond until higher RPM's? For me I would say I can rule out vacuum leak, manifold pressure leak but I need to find someone in Charleston SC to test my N75 and MAF. Also, has anyone had any Limp issues due to a MAP sensor?

Could anyone with a healthy TDI tell me pressures I should see at the VNT actuator based on throttle position. Also, shouldn't pressure coming from the pump change with engine rpm. I have yet to hear a good description of how the N75 operates with respect to throttle response so I can only assume what pressures in the vacuum system should be.

 

[rubadub]

FYI, if anyone wants to understand WHY and how the system operates check out this page.
http://uk-mkivs.net/forums/t/353504.aspx

 

[uzi_cupra]

your actuator length is way too long - it should begin to move at 2-5 inHg on the pump, so make your actuator length shorter and then fine tune it using vag com group 11. you want to see between 70-80% D.Cycle at 4000 rpm in 3rd.

 

[rubadub]

Uzi, this was my problem. I calibrated it as best a could with it starting to move around 2" and bottoms out around 17-18". I am so thankful for this thread. If you are doing this job go ahead and remove the hard pipe going into the turbo, the 90 degree hose off the egr and the heat shield for the passenger side axle. It will make accessing the actuator a lot easier from the top and the bottom.

 

[vtveg]

Diagnostics question:
03 has had over-boost issues since we bought it this summer, which have gotten slowly worse. Car is generally pretty gutless, but definitely has the limp mode thing going -> definite loss of power if you ask too much from it and then its absolutely useless (like slowing to 45 on a big hill on the interstate.)

Finally borrowed a vacuum gauge from a friend today. With the car idling at startup,
26 inhg at the hard line.
26 inhg at the going to the vac port into the n75 valve, which held for 10+ minutes after the car was shut off.
steady 14 inhg coming out of the out port on the n75 regardless of my wife revving car

Based on this I'm guessing that the issue is a dud n75 valve which isn't correctly modulating the vacuum to the actuator. It was my understanding, although I can't tell you from where that the n75 valve should at idle supply the full 25"hg? Am I off my rocker?

 

[whitedog]

Vacuum gauge won't tell you much beyond the fact that you have vacuum. Just sitting and revving won't cycle the turbo since it needs a load. You could tee in and use a long vacuum hose to watch vacuum to the actuator or just get a vacuum pump and cycle the actuator that way. Often, if the bottom engine cover is missing in the salt states the actuator rusts out. You need to see if the actuator moves, when it moves, when it stops and if it holds vacuum.

 

[rdkern]

I would think that the N75 valve is having a problem. It should provide you with the same 26 at the hose going to the VNT that you're getting at the input to the N75.

Did you try to move the VNT actuator with vacuum? As whitey says, it should move and keep the vacuum for quite a bit.

Do you have VCDS? If so, you can test this again, with the VCDS telling the N75 to open and close the VNT, which, with the vacuum gauge, you can see if the N75 is responding correctly.

If I were in your situation, and didn't have VCDS, I would swap out the N75.

 

[whitedog]

You can also swap the two solenoids back there. One runs the VNT, one runs the EGR and even though they are different colors, they work just the same.

 

[mecne]

no more Gutless Golf

Thanks for this amazing Guide ..

Just finished troubleshooting (started a week ago) and fixing my Turbo Issue on a 2000 Golf I bought a few weeks ago. I knew when I bought it , that it had a turbo issue .. how could ya not by driving them without a working Turbo.
Vagg'd it before I bought it as well and with the code below.
Code -
1 Fault Found:
17964 - Charge Pressure Control
P1556 - 35-10 - Negative Deviation - Intermittent
Log Graph of before .

Boost Actual Yellow line .. not much movement there..

1- Tested Actuator with mighty vac .. ( A must when doing this) not holding vacuum.
2- Tested and pulled an actuator off a turbo I had in the Shed.
Change it and run new vac hose .. Test from up top and movement at -5 inHg, and be on the stop (fully open) at 18 inHg. All good ..
3- Connect and start the car .. Vag into Engine , Basic Settings and 011 .. got small movement .. DOH!!!
4- Swap the N75 from one I had in the shed .. Nothing .. Mighty Vac top vac line .. Nothing ..
5- Start replacing Vac hoses .. break the nipple off on the hard vac hose from the Pump to the Brake booster .. DOH!!!!!!!
6- Back to the Shed ..
7- Replace the Hard Vac hose .. connect Mighty Vac .. and bam .. 25 inHg on the gauge .
8- Button everything up ..
9- back to Vag with Basic Settings 011 .. Full range of movement .. and can hear the pressure difference ..
10- Test Drive .. that's the way it's suppose to pull ..
Bingo bango bongo .. All fixed ..
Log Graph of After

 

[CWI_TDI]

Would anyone have a theory about outside air temp and limp mode frequency? My experiences are that it drops into LM when the temp is 35+/- 5 deg F but in the afternoon, as much as I try, I can't get it to do the same. I commute 70 mi one way in NorCal and have a fairly steep, approx 2 mile incline, where it occurs most often-and more often when traffic forces me to slow down below 2500 rpm and then try to accelerate. Often traffic allows me to do the return trip(opposite incline) up thru 80+ mph without any issues in the afternoon. It throws a P0234 code when it goes into LM. I cleaned the MAF last summer w/MAF cleaner and seemed to help at the time. Just wondering if isolating temp as a factor could lead me to a faulty component.
03 TDI ALH, 188k mi
Thanks for looking.

 

[MCR]

@ CWI_TDI: That is an overboost code. So, yeah, the colder air is higher density, and would be easier to overboost than a higher temperature afternoon trip. I'm no guru, but I would look get a Mityvac and verify that the VNT actuator (a vacuum actuator with a nipple that faces downward attached to the turbocharger) has free motion. Also, the vacuum line could be leaking and need to be replaced. The VNT Vanes are normally in low speed position, and move to reduce boost as the boost grows. Yours are probably not moving as the boost grows. Options are (1) actuator is leaking (rubber bladder cracked?), (2) vacuum line is off or leaking, or (3) the linkage is rusted and needs to be moved and lubed.

 

[JohnnyChimpo]

Anybody know if a code P0135 HO2S heater circuit fault will cause a limp mode? Got an '04 Golf BEW that has no power, will only idle and has this code. Happened at the same time the lift pump failed. Weird.

 

[CWI_TDI]

Sorry, maybe a dumb question but if I pull 20in vacuum at the actuator and it drops to 15in about 10 mins, is that considered a leak, or, is that a generally accepted drop in vacuum, or, should it hold indefinitely? ( I read all 26 pgs of this but I don't think it's been specified)
If a leak...then could someone share a technique on how to get the e-clip off the actuator..(more importantly, how to get it back on)...any special tools, mini- needle nose, picks...a 3rd an 4th arm, etc...without pulling the intake, etc? thanks again

 

[whitedog]

Get a big, white sheet and put that under the car. Use a pick to remove the clip. Find the clip on the sheet, somewhere.

 

[Stopp700]

Canadian Grizzley, thank you for explaining in detail the cause(s) for Limp Mode in the TDI Jetta. After dicussing this with my mechanic and showing him your explanation on how to fix the problem it was easy for him to figure out that I had a bad Actuator. Just like you said the VW Dealers did not want to sell just the Actunator. He ended up buyiing one from a parts store on the West Coast. Saved big bucks!!! Thank you again!

 

[flashmayo]

One thing I learned troubleshooting a limp mode issue over a couple of years is that if your ECU is not getting a good clean reference voltage it will cause you all kinds of headaches. I found this when the battery that my car came with got old enough to cause slow cranking in the blistering cold of a CA morning. Replacing the battery has eliminated any sign of limp mode. Of course I had replaced vacuum lines, cleaned intake, replaced MAF, replaced N75 etc in the course of troubleshooting the issue.
So, check your charging system and grounds, and verify that your battery is the proper battery for the 1.9.

 

[pandsa]

Looking for tdi guru for turbo repair

Cel is on and have p1556 and p1557 code. Looking to find a good mechanic in Saskatchewan for help with repairs. Does anyone know of one or where there may be someone close. Thx.

 

[Krytie TV]

From reading the OP, am I to understand that a disconnected hose at the bottom of the air cleaner container can cause an overboost enough to shut down the turbo?

 

[rdkern]

Are you talking about the one from the air filter to the N75? That just provides "clean" air to the system when the switch wants to close the VNT system. You might get some dirt in that way which could wreck the N75. Just the disconnect shouldn't cause an overboost.