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

[BdubsVdub]

and you can do all that with a vacuum pump like the MityVac...in the meantime, just select a lower gear moments before you have the impulse to gun it up a hill

Too bad...it's an auto!

I was wondering if based on the code, someone knew whether it was Intermittent, Negative or positive, as outlined in the post...just to help me in the direction of diagnosing.

It's seeming more and more evident that I should pick up a MityVac...

Thanks!

 

[rdkern]

Limit exceeded - too much boost. Problem with controlling the vnt, N75, lines, or sticking vnt. I guess it's "positive".

 

[Lensdude_com]

the only way to rule out vacuum leaks is using a vacuum pump with a pressure gauge and your problem smells like a vacuum leak.
...and you can use the MityVac on your next car with a manual trans

 

[BdubsVdub]

Haha. Thanks! Do you think a vacuum leak can contribute to less than impressive mpg? I know the auto will Lol but I'm avg 36mpg...just filled up today got 34.

 

[dieselboy04']

Over boost is deviation positive

Sorry my phone didn't take me to the last page before I replied. I would imagine mpg would suffer. I have deviation negative and I've had a best of 47 mpg and now with this boost issues I've been seeing as low a 33 mpg. It sucks. Still trying to find the issue.

 

[chickenhawk]

Hi,
My wife’s 2003 Jetta has been experiencing limp mode, 120k miles. I’ve read through portions of this thread numerous times. Yesterday I threw my hands in the air and brought it to a mechanic.
The car was throwing no codes. I replaced all the vacuum lines as it seemed to be worse the hotter it got. Nothing changed. I swapped out the NP75 dealio with the other solenoid and still no difference. The actuator was pretty rusty looking so I threw a new one of those on(I could barely get the old one to move when in my hand). I thought that might be my problem, but no, still no boost. I read about the oven cleaner trick, tried that, still nothing. The impeller on the exhaust side moved freely before I did the oven cleaner method.
So it took awhile for the mechanic to figure it out. Because it was blowing blue smoke out the exhaust he came back and said it could be 2 things, worn rings or clogged intercooler. Turns out the intercooler was full of oil. He told me the oil was coming from the turbo, worn seals.
Sound right?
So, not one willing to piss away over $2k, I’m looking at options and I have questions. I have heard not to buy a remanufactured turbo. Is that true? I can get a new aftermarket turbo and intercooler off of ebay for under $500. Total crap? I can buy a new Borg Warner turbo off of ebay for $750, aren’t those OEM?
Part of me is afraid to do any work in this car myself, not that I can’t do it but this car seems to want to be the death of me.
Any insight fellas? Do I need to replace the oil lines while I’m in there? Other than the exhaust manifold are there any other gaskets I might need?
I appreciate your time and comments.
Walter
I thought about starting a new thread but thought I would keep it here incase my scenario might help someone else.

I'm back! After letting the car sit for a few weeks, I told my wife we needed to make a decision. Right or wrong it was going somewhere. We have a new VW dealership in Missoula. I heard some of the mechanics came from a reputable VW shop that had dissolved last year here locally and went to work there. I let them know my apprehension bringing the car to them. That was Tuesday. I'll be picking the car up today hopefully fixed. The diagnosis was a 60% clogged air intake manifold and faulty MAF sensor. I argued that a MAF sensor would have thrown a code but at this point I'm over it.
Thanks for all the guidance but this one was past me. If this turns out not to be my problem, I will report back.

 

[octy900]

p1557 etc etc overboosting.

Guys this has to be THE most irritating fault code to find the cause of i'd say.
I have had more of these than hot dinners now & it really is a logical thing to sort (so to speak).Theres only so many things it can be:
1.The least expensive repair for overboosting is probably your vacuum lines. Dont just replace the ones you think are suspect.REPLACE EM ALL!! Same goes for the check valve.dont clean it,just replace it,its not expensive after all.
2.Next is n75 valve.you can try swapping over with the EGR valve & see if that makes any difference to your overboosting fault.
3.Also check your n75 wiring to make sure theres no dodgy connections
4.a failing MAF sensor can also have an affect on n75/turbo boost so try swapping over MAF sensor from another car to see if that changes anything code-wise.
5.Last but not least:Turbo vnt has sticky veins. You can try the mr muscle method of cleaning but in all honesty it'll come back again in couple months or sooner.So best bet is to remove the turbo,strip it down & clean,decoke everything & reassemble.BUT....If youre going down this route you're probably best having your turbo rebuilt if veins are in a bad way etc.
6.If you're getting the overboost code after a rebuild,chances are that they've not calibrated the actuator properly & it needs doing again.(It happens a lot nowadays).
ps:to the above post,Im not convinced your inlet maniold had anything to do with code.MAF maybe though. Did you replace with Bosch MAF or cheap one? If cheap one,it'll reappear i think

 

[chickenhawk]

I barely made it to the dealer. The car had no power what so ever. My intake manifold was restricted to about the size of a quarter. It was throwing no codes. When the dealer told me it needed an new maf sensor, I didn't argue and told them to go for it. It sure hope they used a OEM maf sensor.

 

[alphaseinor]

The dealer will only install an OEM MAP sensor. Those rarely fail BTW.

 

[whitedog]

But MAF sensors do fail.

 

[scottyvdub]

After spending a lot of time and money on my MK4 TDI limp mode issue I finally came upon a resolution! This may not be for everyone but certainly wanted to share the info in case it can help anyone else.

I first replaced the MAF (it was bad because my cruise wouldn't work) , I then replaced step by step my N75, N18, all check valves, all new turbo hoses, new turbo actuator, I cleaned out my intercooler, even checked the MAP sensor... it turns out that my new MAF was sending it into overboost, thus shutting off the turbo under load - usually when I was driving up a hill or trying to pass at 120 on the highway.

In the end, my mechanic logged it with a VAG and reprogrammed the MAF to come on less strong. I now have a bit of lag when shifting gears, but more torque band in my mid RPM levels. And guess what.. no more limp mode! It's been 6 months with no issues.

 

[JerryC]

2002 ALH 184.7K miles. Recently started smelling diesel exhaust inside car. Then noticed brief period of "limp" mode lasting a few seconds, then CEL light eventually came on P0234, overboost turbo situation. Went through some of the great posts on the forum. Did change the MAF sensor and ordered a new N75 valve and began researching best places to buy or at least learn how to clean turbo. I spoke to my long time friend, Master VW mechanic Tom A. who also suggested checking the EGR valve for build up. There really was not much in the way of debris/blockage. Valve seemed to be able to move freely. While looking at the back firewall, I noticed where the wiring that went to the EGR valve had 1 (out of 2) frayed wires. I resected the 4 inches or so of bad wire and soldered in 4 inches or so of about 20-22 gauge wiring connected by butt connectors and covered with corrugated conduit. Erased the code. Test drove. And test drove, And test drove. No return code! The diesel smell is gone, and the sound of the turbo working properly has returned (I have not heard it in some time). I suspect rodents got in to the wiring. Take home lesson for me: in addition to the beautiful write up by Canadian Grizzly, I think it might be fair to add bad wiring to his list of things that can cause P0234 overboost situations: Bad Maf (oxygen sensor), Vacuum leak, Faulty N75, Bad Actuator, Gummed up turbo. Check the wiring too!
This is my first newby post-so please go easy on me!
I have read this great site before, and have changed my timing belt using the technique described step by step in this forum about 18K miles ago- started right up!
I am a non-mechanic, but I want to thank all of you for your insights over the last few years.
Jerry C

 

[TDIdiot]

Okay, I going to post this here for lack of a better place to put it, but at 31 pages in, I don't know if it will ever get seen. Perhaps some admin can suggest a better place?

You may learn from my experience!

I have a 2003 with the 1.9l and about 315,000 miles on it. Regular oil change, yaddayaddayadda. At about 240k miles, it started not performing so crisply, and around 280k it started slowing on hills, and at about 295k one of the valves on cylinder 1 went pear shaped. A local German specialty shop rebuilt the head and off I went.

Shortly after the rebuild, my wife wanted to move the car. "The key's in it." She came back and said it wouldn't start. What? It has never not started. On a lark, I recalled that I had bought a replacement fuel filter because I did not remember ever having replaced it, so I reached down on the bottom of the fuel filter and drained a little (probably not the best idea) and it started right up. So I replaced the filter and then spent a week fighting the fuel leak and then finally replaced the thermostatic T and the leak went away. Suggestion #1: if you replace the fuel filter, buy the T at the same time. It doesn't cost very much. You may not need it, but how cheap do you want to be? Also, read up on purging the air out of the lines before you start

For a very short while after that, it seemed like some of the torque had returned, but it was not much and short lived, so I have been trying to decide what to do with it. Finally, I decided to see if there were some simple things I could do and started with these:

http://www.myturbodiesel.com/wiki/low-power-constant-tdi-engine-repair-and-solution/
http://www.tdiclub.com/TDIFAQ/TDiFAQ-8.html#e

I hooked up the VAG-COM USB thingie and started down the list. MAF sensor was good, check that off the list. Boost ... what the heck? There was absolutely so boost no matter how much boost was being requested. So after a quick glance around the vacuum hoses and the Bentley manual, 1 thing was clear (and it was not the manual): a hose was missing. I would have said 2 things were clear, but I think the Bentley has an error in it because the N75 diagram for the 1.9l is opposite the 1.9l PD.

I found the missing hose, hooked it up, and started the car. Immediately, it was noticeably smoother running at idle. The hose had a kink in it, so I suspect it is leaky. The order has already been made to McM-Carr per the OP. I then took it out for a spin, and here is where my troubles got ... interesting.

Right away, it was clear that some torque had returned and also that the brakes were working better. Duh - vacuum boost on both, right? So I got on the freeway. While shifting from 4 to 5, the engine just went straight to redline and didn't stop. I mean, I took my foot off the gas, and then turned the key off, and then turned it back to the ON position, and then turned it off, and then took the key out. Black smoke was pouring out the back, I'm doing about 50 on a merge lane on a bridge going over a river, nothing will stop the engine, and now the steering wheel is locked because I'm holding the key in my hand. Fortunately (or perhaps not so fortunately), I've been in similar situations, so I was more perplexed than frightened. The engine finally stopped (starved of fuel, I suspect), but the black smoke kept coming. I glanced at the fire extinguisher, turned on the E-flashers, got out and popped that vacuum hose back off, and went home without further incident.

My theory is that the vane actuator and/or the N75 had not been used in such a long time that gunk had built up on it/them, and it/they got stuck when I was accelerating onto the freeway and the car was requesting full boost for the first time in a year or more. When I got home, I put the hose back on, revved it to 3500, saw no more sticking, so I put the VAG-COM back on to log it if it happened again, and took it out for another spin. No problem the second time around, so ... we'll see. In any case, it ran much better, but I'm sure the full vacuum hose replacement will be a good move.

[UPDATE: Turns out that this may have more to do with oil built up in the intercooler plumbing. It still starts cold, so possibly no damage done. Suggestion #5: check the intercooler once in a while. See http://www.tdiclub.com/TDIFAQ/TDiFAQ-7.html#f]

Suggestion #2: diagram your vacuum hoses prior to any major surgery. Replace them at around 240k miles. The Bentley manual is lacking in this regard and may have an error on the PD diagram (it shows the PD N75 gazinta and gazouta opposite to every other diagram I have seen, the placement of Ts is inconsistent, etc.).

Suggestion #3: baseline your MAF and boost performance with the VAG-COM logging function early in its life. Check it out regularly. Don't wait until you're just fed up with it. I never got a single DTC for this problem, so it appears to have been a combination of worn vacuum hoses and possibly carelessness during the head rebuild. The change was a mixture of gradual and correlated with other events, so it felt like the result of unavoidable wear and tear.

Suggestion #4: Start with TDIClub forums and work your way back to the dealer as a last resort.

 

[nodrog]

great write up. followed this guide and no more limp mode. problem was leaking vacuum pipes. changed pipes, no more limp mode, great. mechanic wanted to change turbo at cost of silly money. did the job myself at cost of £20.00 for new silicone pipes and an afternoons work. thanks again for a great write up.

 

[mloecher]

Hey guys, here is a similar (sorta) issue maybe someone can give some insight on

I own a 2014 Jetta TDI manual with about 8k miles, during attempting to install a Chinese push button starter + Directed PKE lock/unlock fob. After I probably shorted something the electrical system went crazy and since then the car seems to be in a sort of a “limp mode”.

Took it to the VW dealer and they claim the non OEM radio did it. They suggested buying a new ECU because they are not getting a read from the ECU on the diagnostic. I believe it’s a fuse / relay short but all relevant fuses seem to be ok visually, not tested yet.

Symptoms are:
Many orange dash lights stay on in the instrument cluster (brake, power steering, ABS, traction control …)
After I manually jumpstart the car it drives well, the glow plug light is constantly flashing and check engine light flashes for about a minute then turns off. When the car drives it doesn’t seem to lose power (Turbo seems to kick in properly)

All 4 corners hazard lights stay on, alongside DRL lights and rear brake lights.

No power steering
No cabin lights
No A/C
No heated seats
No horn or turn signals
No radio

Light switch works on/off. hi/low beam
Instrument cluster works fine and shows mph, mpg, temp…
Reverse lights work when putting gear into reverse.

Any thoughts ?

 

[alphaseinor]

My guess:
You plugged in the Blue/white wire from your radio (labeled power antenna) into the harness that goes into the car, it should not be plugged into the harness.

You'll also need someone to clear out the codes in all of the modules, look for someone with a VCDS

probably not related to this thread

 

[ddunfee]

I have a 2004 Passat TDI that will show po101 code when started or sometimes when slowing down. Both times I supposed that the turbo shouldn't be working. Checked vac lines with mighty vac and range on VNT. Look/listen for leaks for boost. Replaced a plastic line after the intercooler a couple years ago when I was getting underboost but at that time it would return right away. This time you could go for days without it or it might return on mild to brisk acceleration. Never on hard acceleration.

I did change the relays that controls the fuel pump. Any ideas?

 

[alphaseinor]

P0101 is Mass airflow sensor code, usually I find the cause is not a mass airflow sensor itself, but the connector for it. (although it still could be a mass airflow sensor, just very rare).

 

[ddunfee]

I forgot to say that I did replace the MAF sensor. I will try to check the connector and put some dielectric on it. Thanks

 

[ddunfee]

I cleaned the connections with a alcohol pad and put some silicon dielectric on it. No code for a couple of days then when I came to a stop at a light I got a workshop emissions which was a po101. This doesn't happen very often but I have to keep my code reader plugged in all the time. Very frustrating

 

[Lensdude_com]

I fill the MAF electrical connector with dielectric grease...and all the others under the hood

 

[ddunfee]

Well I didn't fix my 101 problem but I did pick up a 203 problem. Gotta love VW

 

[PrintSmith]

I'm getting P0299. My reader is spitting it out as an undefined fuel air mixture error. I've done the easy stuff, replaced air and fuel filters, replaced vacuum lines, with no resolution. Last night I put tape around the connection at the vacuum pump and drove it home and to work this morning with no problems. Today the problem returned.

I live in the Denver area and yesterday the temperature was below freezing. Today the temperature is closer to 60*F. Does the temperature difference give any additional information to help offer a course of action based on the wealth of experience here?

Have a vacuum tool lined up for tomorrow to check the actuator, but any additional thoughts/suggestions/ideas will be greatly appreciated.

Vehicle is an '03 Jetta TDI - ALH motor - 430K on the clock. And no, that's not a typo, 430,000 miles on the odometer.

 

[alphaseinor]

http://wiki.ross-tech.com/wiki/index.php/16683/P0299/000665

Basically follow the instructions on this thread, it's pretty methodical. you have an underboost condition

Glad to see yours is over 400k Mine ended up with 780,000 before it got wrecked, so... YMMV but it ran great until that time.

 

[PrintSmith]

Will have to show my wife your reply when she asks if it's really worth fixing the car next time. Thanks for the reply alpha. I was hoping maybe the temperature variation might help in diagnosing the issue by someone with more knowledge than I have, which is probably just about everyone here

 

[rdkern]

Do you like to work on cars?

If the temperature had an impact, it would have kept a boost hose from opening due to the stiffer rubber due to the cold. This is not necessarily the cause, but it could be influenced by the weather.

Follow the boost system around your car and see if you find either a disconnected tube, or a spray of oil. The oil will lead you to the point of failure.

This is a case in which a VCDS might be of help in testing the actuator and EGR.

If you can, start by looking around the boost system. It is one possibility, and might not cost much to fix.

 

[PrintSmith]

Yeah rd, I like to work on vehicles as long as there isn't a time requirement associated with it, which unfortunately isn't the case this time around. This is the only vehicle I have running at the moment and I need to get back and forth to work at least one more day this week before having the weekend (and hopefully some nice weather) to do some of the more involved examinations if they become necessary. No garage and winter in Colorado aren't what one would call ideal conditions for an involved repair, but you gotta do what you gotta do . . .

I'm fairly certain it's a vacuum issue of some sort. I had the brake system act like it was missing the assist a couple of times in the days leading up to the appearance of the P0299 code. I might be off thinking along those lines, but it seems the most reasonable explanation.

That I made it home and back to work this morning with no codes after wrapping tape around connection at the vacuum pump last night gives me some hope that the vanes in the turbo and the actuator aren't the source of the problem, but with the miles I have on the vehicle anything is possible at this point.

 

[rdkern]

It could be vacuum related, since you need vacuum to open the vnt and allow boost. However, without boost the car should still run, although rather poorly.

If the brakes are giving problems, it would certainly be appropriate to get them fixed first. It's more important to stop than to go. Fixing them might also fix this issue.

 

[PrintSmith]

Brakes work great - just a hard pedal from lack of assist a few times in the days leading up to the P0299 code first appearing.

Car is running in limp mode when the P0299 code appears, otherwise seems to be fine. Last night it went from 5300' to 8500' in elevation, up Bear Creek Canyon for those who live in Colorado, in 5th gear the whole way, which is normal. Will see if it does the same tonight with the sun down and temperatures falling.

 

[PrintSmith]

How difficult should it be to move the actuator and vanes by hand while the everythng is still attached and the motor is off? Should it move very easily or should there be some level of resistance?