[JayKCee]

Right .. 2008 2.5 Touareg

I get the flashing glow plug / workshop / limp mode thing that resets after i switch off and on again ..
"I have checked ..."

The actuator on the turbo and it appears to be moving just fine ..
Ran a test in VCDS to cycle the N75 boost control valve while i monitored the Vacuum and watched the actuator arm move in and out .
( appears to be fine )
Checked for a leak in the vacuum lines ..with a vacuum gauge / pump ... even tried a smoke test on them .
Pulled off the air intake after the maf and treated the system to my home made smoke machine ... no apparent leaks either ..

Its an intermittent fault , other than when it hits limp mode the car has a ton of power ..
Only common factor is it only happens when the car is warm ... ( normal temp )

Please someone , anyone , HELP .....its driving me nuts

 

[TurboABA]

16683/P0299/000665 - Boost Pressure Regulation: Control Range Not Reached
Possible Symptoms

• Reduced Power Output
• Limp Mode

Possible Causes

• Hoses/Pipes incorrect connected, disconnected or leaking
• Charger Pressure Control defective
• Turbocharger faulty
• Diverter Valve faulty

Possible Solutions

• Check Hoses/Pipes to/between Components
• Check / Clean / Replace Charge Pressure Control
• Check Turbocharger
• Check Diverter Valve

Special Notes

• If the Turbocharger is faulty due to mechanical / internal problems or the exhaust system is restricted (typically the Catalyst) this fault may be the end result.

 

[JayKCee]

Hi and thanks for the reply ...

Symptoms ... ( when the fault happens ) yes

Causes ....
Hoses ..etc ....smoke machine would have shown that
Pressure control ....checked with VCDS

Diverter valve ? where is that ?
Turbo faulty .. ? But operating normally 95% of the time ?

Notes ..

Exhaust system / DPF ... ? unlikely I do long drives every day and its happened on a motorway when I was expecting a possible regen .... kept it at a constant 70mph for 30 mins ..
was going like a train ..and then it came up with the fault ..

I've heard something about faulty exhaust pressure sensors might that be related .?

 

[Gnits]

V10 Vac Diagram? and P0299 underboost.

Hi all, Been searching the site here looking for info. Recently, I've been getting some intermittent P0299 underboost errors on the Engine 2 side. I checked measure block 11 and the boost appears low but is following the request normally. From searching, it appears this may be an issue of leaks...

www.clubtouareg.com

 

[JayKCee]

Hmm funny you should mention that ...I was hoping to have some time tomorrow to test that using block 11 and run a graph ..
I only pray its not electrical ..

 

[JayKCee]

Was up to my tonsils today so I didnt get a chance to do the tests ....hopefully tomorrow or Saturday I will and I'll try to have the data to upload
Thanks for the pointers so far guys


Ohh one thing I meant to mention is that I have noticed it NEVER happens if I'm zipping along , twisty roads , speeding up , slowing down ..accelerating ..etc
It only ever happens ..as in every time .....when I have been keeping a steady speed for longer than 5 mins or so ... I've experimented a little while driving
and if I give a bit extra throttle now and again ( every 30 seconds or so ) it wont throw a code or go into limp mode.
almost as if I force the actuator to move under load its ok ...but if it rests for a while it sticks ... just a wild guess.

cant figure that one out but it might ring a bell for someone ..
Jay

 

[redbarron55]

Try checking for a leak with a Mighty-Vac with the vacuum gauge connected directly to the diaphragm on the controller.
Pull a vacuum to full travel and then make sure that the gauge remains steady and the shaft does not leak down.
I had a 2009 JSW TDI that had a leaking actuator and it did pretty much that very thing.

 

[JayKCee]

Ha .. Mind reader ...

I did exactly that yesterday afternoon by disconnecting the vacuum tube from the N75 to the actuator and using the original tube pulled a vacuum which easily moved the arm ..and it appeared to hold the vacuum. Then figuring that I had noticed that only after a few mins at the same speed / load /rpm does the problem ever occur ... I stood watching it slowly bleed off over 2 mins .. by that time it had dropped by 20% ... so I have replaced that particular pipe with a silicon one to test .. ( I guess 11 year old rubber pipes may not be 100% any more... )
Results so far ...car seems more responsive ...only time will tell if its a solution ..

BTW ..was your as sporadic as mine ...eg . not acting up during spirited driving but spitting the dummy during steady cruising ?

I would have posted test results of my runs except for some reason my vcds has decided to have a fit with many of the options greyed out and unavailable ...I'm looking into it .

 

[Gnits]

Vacuum is regularly "vented" by the control systems of the car as part of their normal operations, but is also continuously upheld and re-generated by the vacuum pump in the car at the same time. Because of that a slow leak that only results is 20% loss of vacuum over 2 minutes in a static test at any particular pipe can not possibly cause any noticeable malfunction in the system by itself.

 

[honebone]

My wife’s 2014 Treg tdi has done the exact same thing twice in the last 2 weeks. Each time we continued to drive it in limp mode (w/ flashing ! symbol) to our destination and shut it down; each time we waited about an hour, started it up and had a perfectly running vehicle with no ! symbol, no limp mode. First time I took it to the closest Advance Auto; their scanner read no codes. Second time I was closer to a VW dealer which plugged it in and found the reduced boost code. They cleared the code and we’ve had no problems since, but we haven’t driven it in the same long distance, same speed mode we did when the problem occurred before either. The dealer didn’t charge us for their time, nice, but did say that if it continues they recommend bringing it in to have them go over the entire turbo system to look for vacuum leaks, faulty turbo, etc. We bought this vehicle a little more than a year ago as a CPO but don’t believe whatever time they spend looking for problems would be covered but am not sure about parts cost if they actually find anything defective. We both love this vehicle but my wife will not put up with this continuing to happen. I’ll keep tuned to this channel to see what info you find...

 

[Gnits]

Over and under boost fault codes are automatically cleared at engine shutdown. However, that doesn't mean that they're not real, and if they appear sporadically, that's usually only because the boost leak is only close to the fault threshold, but not always hitting it - and not because everything is just fine with the engine. Also most boost leaks get better (ie. mostly disappear or at least decrease in severity) once the engine has warmed up, because of thermal expansion which mostly seals typical small cracks.

 

[JayKCee]

Vacuum is regularly "vented" by the control systems of the car as part of their normal operations, but is also continuously upheld and re-generated by the vacuum pump in the car at the same time. Because of that a slow leak that only results is 20% loss of vacuum over 2 minutes in a static test at any particular pipe can not possibly cause any noticeable malfunction in the system by itself.

Really ?.... I never heard of that before ./.. So a question ... If the vacuum is purged every so often why doesn't the ecu pick up on it 's sudden lack of boost when that happens ..?
Not doubting what you say but astonished and confused. Sounds more like what a blow off valve does to relieve excessive boost in systems that use that.

I measured that loss of vacuum over 2 mins ... but I'm pretty sure that at the rate it was dropping it would have been close to 50% in 4 mins ... which surely would have triggered something.

 

[JayKCee]

Over and under boost fault codes are automatically cleared at engine shutdown. However, that doesn't mean that they're not real, and if they appear sporadically, that's usually only because the boost leak is only close to the fault threshold, but not always hitting it - and not because everything is just fine with the engine. Also most boost leaks get better (ie. mostly disappear or at least decrease in severity) once the engine has warmed up, because of thermal expansion which mostly seals typical small cracks.

In my case ... The problem never occurs when the engine is cold ... I need to be driving at a steady pace for a while ( normal engine temp ) before it happens ..
I love the car but this is like getting poked in the eye every so often .

 

[Gnits]

Really ?.... I never heard of that before ./.. So a question ... If the vacuum is purged every so often why doesn't the ecu pick up on it 's sudden lack of boost when that happens ..?

For one, the first part of the question has nothing to do with the other. This means that the working of the vacuum system is not directly connected by turbo boost, or problem detection. Actually, in most Touareg engines the turbo is actuated electronically (ie. using a stepper motor of some kind) and not using vacuum lines / solenoid / actuator, so, problems with the vacuum system can not possibly affect or cause turbo boost problems.

Also, the vacuum is not "purged". It's just that parts of the vacuum system are pressurized (ie. atmospheric air is let in), then exposed to vacuum again, then pressurized again, etc, as needed, as part of their normal operation. That's for ex. what the N75 solenoid valve does, which controls the turbo boost. It switches between the vacuum going from the valve to turbo actuator being connected to that part of the vacuum system that's persistently under vacuum, and between the atmosphere, which is essentially an unlimited supply of air with ~1 bar pressure.

Also, the engine is not boosted all the time. When it's not, the vacuum that was previously in the turbo control vacuum lines is "vented' (ie. pressurized air is let in, which moves the turbo vnt control rod in one direction), and when it needs boost again, the air is sucked out and this vacuum is re-established in it (which in turn moves the turbo vnt control rod in the opposite direction). So, it's perfectly normal to not have vacuum in the turbo vacuum lines at all times, even if the engine is working perfectly.

And the thing with "the ECU picking up on sudden lack of boost is", that this never happens. The ECU never raises a fault just because there's a "sudden lack of" anything (with the exception of the very few time critical systems, like airbag deployment and such). Instead, the out of bounds condition has to 1. persist for a specific time, and 2. be higher or lower than a pre-set threshold to actually raise a fault code. That's because the car's system are not working perfectly precisely at all times, and not even working always the same, because for ex. environmental conditions like ambient temperature, humidity which all affect the exact working of this or that, or because of internal factors, like voltage fluctuations or certain modules encountering a fatal error and "rebooting" themselves.

So, the system is working with tolerances and doesn't immediately raise a flag whenever something does not go exactly as expected, because that really happens all the time, and keeps happening more and more often and in more and more severe manner as the car ages, and several components wear or get less reliable. The car has to cope with that fact, and can't just keep throwing a hissy fit, just because some components have worn down, and not working precisely as they did originally. The car just can't start throwing fault codes just because something is not exactly as it expect, especially not as long as it can compensate for the difference, or said difference between expected and actual values doesn't exceed the pre-set tolerances.

I measured that loss of vacuum over 2 mins ... but I'm pretty sure that at the rate it was dropping it would have been close to 50% in 4 mins ... which surely would have triggered something.

The point is that in the car the vacuum is regenerated all the time, ie. the vacuum pump is sucking out air of all the parts of the vacuum system that are currently connected to it some way. And because of that if there's a small leak (like something that 50% in 4 minutes thing, which is really nothing, because a severe leak would be loosing like 100% of vacuum in 4 seconds or something), that can never manifest itself as an actual "vacuum leak" that somehow hinders the system from working properly, because the small amount of air that the leak lets in is immediately removed from the system by the vacuum pump, and thus can not possibly affect or hinder the working of the car.

 

[JayKCee]

Thank you for that .... With respect , I truly wasn't expressing disbelief in your input ... I was simply stating that I was not aware of what you were saying.

I understand that an engine isn't in a boost state all the time ..
However .. if we assume that if its been driven in a manner that requires it to maintain a particular rpm for a prolonged period some form of boost is being applied or controlled to control the turbo via the actuator rod .. ? Otherwise when we cruise , we are basically operating as a 5 cylinder Naturally aspirated diesel engine ..you can see why i came , perhaps erroneously to that conclusion.
The last direct electronically controlled link to boost is the connection to the N75 isn't it .,.. ? AND ...I have used VCDS and a vacuum gauge to interrogate the on / off action of the N75 which it did.
So I'm at a bit of a loss to understand what is triggering the P0299 ...the car is not lacking in power apart from when that fault occurs ..

I apologise in advance if I'm asking stupid questions , but I have been trying hard to diagnose the root of the problem without engaging in the expensive hobby of simply throwing new parts at the car.
I appreciate the input and the time taken to explain things

J

 

[JayKCee]

I realise , that different cars have different systems ...In the case of my car ... the vacuum is applied / supplied to the N75 .. which is then electronically commanded by the ECU to operate the valve ( the N75 ) .. to control the vacuum via a tube to the actuator on the turbo which then works the arm that moves the vanes in the turbo itself.

 

[Gnits]

The last direct electronically controlled link to boost is the connection to the N75 isn't it .,.. ?

Yes.

AND ...I have used VCDS and a vacuum gauge to interrogate the on / off action of the N75 which it did.

Okay....

So I'm at a bit of a loss to understand what is triggering the P0299 ...

The fault occurs because the boost pressure measured by the MAP sensor (ie. "Turbo boost pressure (actual)" or similar in VCDS) falls several hundreds of millibars short of what the engine thinks the boost pressure should be (ie. "Turbo boost pressure (requested)" or similar in VCDS). The engine's "expected" boost pressure values are based on or calculated from the intake air mass, temperature, the RPM of the engine and the temperature of the exhaust, which determine how fast the turbocharger spool and how much air it compresses.

However, this error condition has to persist for longer than pre-determined period of time, and it also has to be more severe than a pre-set threshold (usually 2-300 mbars), for the fault code to be raised and for the engine controller to go into limp mode (which is a deliberate decision by the ECU to limit engine output in order to prevent further damage). So, if the boost pressure only lags a few seconds or it's only below expected by 50-80 mbars, the fault is not triggered, because it doesn't fall out of tolerance bounds, yet.

Now, even though the engine can detect that there's an error condition, but it can't possibly know why it's there, because this type of problem (ie. the boost pressure not reaching expected levels) can have several reasons, like

• the vacuum system not working properly
• the N75 valve not working properly
• the turbocharger not working properly
• all of the vacuum system, the N75 valve and the turbocharger working properly, and proper boost being generated initially, but then escaping somewhere before it actually gets to the intake manifold (ie. having a boost leak somewhere)
• the MAP sensor reporting false readings

There's no way for the engine to verify ("double-check") any of these, or to distinguish between these, and they all result in the same thing: the boost pressure not reaching expected levels. Also, several factors could be adding up, like there could be both a slight problem with the vacuum system or the N75 solenoid valve, and also a slight boost leak (for ex. a crack in the charge air hose) - both of which could be possibly not be severe enough on their own to trigger the fault, but together might "add up" to a problem that's beyond tolerances.

That's where the mechanic/owner comes into the picture, who needs to subject the car's parts and systems to a complex diagnosis to either exclude some of these possible problems, leading him to the remaining culprit(s) by exclusion, or directly confirm the non-working or faulty state of some of these components. This what the smoke test, the vacuum test, the turbo actuator test, and boost pressure log are there for, which all yield information leading to a possible conclusion of where the problem lies.

I hope this clarifies what tests are or might be needed, what's the rationale behind executing these test to find the actual bad part in the car that needs fix or replacement, or why just testing the N75 valve or the vacuum system (especially when taken out of the car) might not be sufficient or might not lead to a positive identification of the actual culprit or to all of the culprits causing the trouble.

.the car is not lacking in power apart from when that fault occurs ..

The car is apparently not lacking of power, because to a certain point the ECU can compensate for the problems. For ex. it can increase the RPM of the engine, increase the duration the turbo is spun for, or start spinning the turbo sooner than would otherwise, in order to still generate the same level of apparent power to the driver; who in turn will not notice any obvious problems with a car, despite some or more parts already not working properly and not performing how it or they should.

But the ECU can only compensate to a certain point - and when it's not able to do so anymore (because some problems get out of tolerance bounds), that's when it triggers the fault code and goes into limp mode. Which, as said, is not the result of the lack of turbo boost directly, just a deliberate decision by the ECU to limit the engine's output to a safe level, in order to avoid further or more severe damage to it.

 

[honebone]

So, Gnits, do you think doing all the diagnosing you’ve described in order to get to the bottom of my car’s problem would be covered under its “fixed tdi”/CPO warranty? Guess I’ll have no choice but to take it in if it happens again, I’m just afraid of being taken advantage of whether or not they can find the cause!

 

[Gnits]

So, Gnits, do you think doing all the diagnosing you’ve described in order to get to the bottom of my car’s problem would be covered under its “fixed tdi”/CPO warranty?

I have no clue. Also, your car's engine is completely different from OP's. They're not even from the same generation.

 

[JayKCee]

Okay....

Now, even though the engine can detect that there's an error condition, but it can't possibly know why it's there, because this type of problem (ie. the boost pressure not reaching expected levels) can have several reasons, like

• the vacuum system not working properly
• the N75 valve not working properly
• the turbocharger not working properly
• all of the vacuum system, the N75 valve and the turbocharger working properly, and proper boost being generated initially, but then escaping somewhere before it actually gets to the intake manifold (ie. having a boost leak somewhere)
• the MAP sensor reporting false readings

That's where the mechanic/owner comes into the picture, who needs to subject the car's parts and systems to a complex diagnosis to either exclude some of these possible problems, leading him to the remaining culprit(s) by exclusion, or directly confirm the non-working or faulty state of some of these components. This what the smoke test, the vacuum test, the turbo actuator test, and boost pressure log are there for, which all yield information leading to a possible conclusion of where the problem lies.

I hope this clarifies what tests are or might be needed, what's the rationale behind executing these test to find the actual bad part in the car that needs fix or replacement, or why just testing the N75 valve or the vacuum system (especially when taken out of the car) might not be sufficient or might not lead to a positive identification of the actual culprit or to all of the culprits causing the trouble.

I agree with everything you said and my understanding of how the various systems interact is the same... and mostly it serves to illustrate why exactly I I'm at a loss so far ...
Because ... Having checked for faults in...........

1- the vacuum system
2-the N75
3- The turbocharger ...............Not sure how I could test that apart from checking that the actuator rod moves through full travel and i have observed it moving via suction. ( I did )
4- I have performed a smoke test on air intake system post MAF .. ---- no trace of a leak anywhere .
5- The Map sensor............... I can clean replace ... or if there is a good resistance range etc it should fall within I can check .
6- As soon as I can manage to get VCDS to stop having a hissy fit ... I will post boost commanded / Actual figures + rpm

As "HoneBone" mentioned earlier ... I'm reluctant to bring it to an official outlet because of my previous experience of them "Throwing new parts at the car"
Also I doubt if they would be overly concerned about the financial results of doing that since its in their interest to do so....but not mine.

Once again ....Many thanks.

J