2.0TDI limp mode Please Help!


Registered User
Aug 8, 2008
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High Wycombe
Hi everyone,

Im a first time poster on this site so sorry if I am not doing things correctly...

Please can someone help I have an A3 2004 2.0TDI DSG, when on the motorway at around 80mph if the is an incline on the road the car goes into limp mode, this is a very frustraing problem as it has been to Audi and Fontain Audi amongsnt many other garages but no one can find the fault, the engine fault code is P0299 overboost pressure regulator range not met....

I have found that if I turn the engine off and back on again it seems to be fine, so far the solenoid block, thrust sensor, MAF, fuel filter, air filter and glow plug (thanks to audi :)) has been changed

I have read about N75 or something but apperntly these were on the 1.9 engines and not the 2.0 engines (my engine code is BKD if it helps) also I have been told about vaines on the turbo but the garages tell me that it shouldnt be that

Has anyone seen this before or does anyone have any suggestions, please help!

N75 is combined into your already replaced solonoid block. Fault sounds like turbo is over boosting and causing limp home mode. If you have VAG com then try running engine. Put VAG com into engine basic setting and select channel 11. Your engine speed will increase and if you look at actuator rod on turbo this will move from maximum to minimum every 10 seconds approx. Look for jerking movement of rod and also listen for excessive noise. If rod not moving check vaccum hose between solonoid block and turbo. Also check for corroding or poor earth points at engine ECU. Should also be able to check boost pressure specified and actual readings via MVBs 10&11 on roadtest with the VAG com.
this is an underboost code not an overboost - it goes into limp mode at around 2000-2200rpm accelerating moderately or up hill, usually in 6th, usually where the acceleration/ rate of change isnt high - if you boot it you wont get a code because the engine makes the requested boost after a short time.

the boost isnt reaching the requested over a certain time period and the ecu assumes theres a fault - causes could be:
are you chipped? far more likely to happen if unrealistic boost requested with one of the following:
boost leak - can be small, often a split small hose
turbo knackered, though not the most likely unless you have other symptoms
boost control valve not working properly - might need replacing

probably a few others as well
awesome! thanks for your help guys!

Dunk the car is chipped, but I had it chipped around 3weeks ago and the fault has been there for coming on 8months now, reason to get it chipped was becasue someone told me it could be ecu and i should get it chipped instead of replaced as it would work out cheaper, i later on found out he was a muppet :)

I personally cant find a leak in any of the pipes and I would have thought that the dealers would have checked for this also, do you have a part code for this boost control valve or do you know roughly what it looks like or what it is and I can try changing that perhaps

My friend had a skyline with a knackered turbo but I dont get the symptoms that he had such as heavy smoke etc.

As me8cat suggested I will try checking out this pipe between the solenoid and turbo also

I think its about time i invested in vagcom :)

Thanks guys appreciate the help so far
the boost leaks can be quite small and difficult to find - you sometimes need to pressurize the system then handle/flex all the small pipes to find a leak

a main dealer isnt going to be bothered about this .

can you change the map back to standard to test? an example of problems would be a remap asking for too much boost plus poor fuel or bio, so the engine cant make the boost as quickly - either on their own wouldnt throw an error, but together its intermittent
the boost leaks can be quite small and difficult to find - you sometimes need to pressurize the system then handle/flex all the small pipes to find a leak

a main dealer isnt going to be bothered about this .

can you change the map back to standard to test? an example of problems would be a remap asking for too much boost plus poor fuel or bio, so the engine cant make the boost as quickly - either on their own wouldnt throw an error, but together its intermittent

I would have to agree with Dunk, boost leak sounds likely & it can be unrecogniseable to the naked eye & only under extreme pressures it shows through given the strength of some of the pipes, need a garage thats not just interested in a big money spinning job & actually does some real mechanical fault finding, no disrespect to any mechanics on here but I do find some tuners have been known to not be interested in the small crappy jobs as not a big money earner.

I have to say my dealings with Fontain has left me feeling they're very stuck up & very greedy, reminds me of my dealings with QST, I was interested in buying a car, wasnt exactly cheap either, they never followed up after initial email to me, they sold the car didnt come back to me to say ok sold can we find another one for you, very highly unimpressed & they are seriously overpriced compared to some others, they may be a well known audi reseller but doesnt mean they have to have that kinda attitude as given todays climate there are plenty who are willing to sell a car for realistic price with far better customer service I can tell yer.
ok, so i changed the map back but it made no difference :-( same P0299 code

Interestingly enough i found a hole about the size of lead out of a pencil in the intake pipe just after the MAF on the pipe that bends round to the left, I have ordered a new one and it should be here tomorrow, fingers crossed il let you know how I get on, if not then pressure test it is

Thanks Guys
duck tape then test again as duck tape is ****** strong & braided, be hard to break through several layers of that mate, just something to try while you await pipe of course, but another thing to use I know people will frown but trust me is loctite superglue on tiny holes like this, this will seal the whole easily cause it actually would melt the sides of the pipe hole only a tiny bit which then makes the sides bonds together & seal as if new, worked for me & no problems after, just few ideas for testing purposes.

Wish it would work on the mouth of my older sister though, but then we're talking dartford tunnel diameter so guess loctite is bit to small for that kinda job, oh well have to be a sniper then, lol, lol
lol, sounds like my sister...

i tried some elecectrical tape but that didnt help :-( i personally dont think it was strong enough because the hole is in one the rigid drops, new pipe should be here today and i will try it tonight

how did you even think of using the loctite :-D
ye maybe they're clones, lol

I did say duck tape, electrical tape wont work u silly ****, lol, duck tape binds/seals better & the glue on the tape seems to bond a hell of alot to almost anything, good ****

loctite or any glue of same makeup actually with alot of plastics & rubber materials seems to melt them to a degree within the joins which makes them bond better as its basically taking it back to when made if you catch my drift remoulding the plastic altogether, the glue also helps it even more of course, superglue is my ultimate no.1 tool in the world as it is amazing, lol, except when it gets on your clothes & sticks your fingers together, lol, but it works unbelievably well

I know it sounds cowboyish & trust me I'm not one at all, but I've used on tyres before & worked 100% mate, failed mot on sidewall of tyre has a slightly cut on, took away glued, left for an hour took back they passed it, lol, same with puncture of course if its not a massive nail cause all the puncture is cause mostly sharp object & the rubber isnt lost just pushed aside, so glue melts it back together as no loss of rubber in 1st place, not I advise this in all circumstances of course, but mine worked & saved me fair bit money over time
lol, nigel your a funny man, anyways back to the problem, changed the pipe made no difference, anyone know of any good place to get the pressure test done, im in high wycombe (south bucks) or i am happy to do it myself if someone would be so kind as to guide me into the right direction :-D

I have a little compressor wack it into the air intake after the maf i guess and see if air leaks from anywhere right? or do i need to do more
blow on the exhaust pipe, lol, ok sorry getting carried away, I'll go stand in the corner

someone will be along soon while I do some googling for answers, lol.

or the next search engine cuil.com which actually provided google with alot of its search engine tech anyway
lol, how about we stick some massive wind turbine onfront of the car, crank it up to max, the generated air will flow through the car and wel see if anything happens? :)

anyway i found this link


that brother seems to have way too much time on his hands but i like his idea..

Im not sure if 10psi would be enough though becasue surely it would have to fill the intake system and all the rest of the stuff back through the tiny little pipes into the solenoid block?

on a seperate note no many of the local garages are too interested in helping out with this, oh yeh and another thing, i just went down the road to drop my friend back home (yes its a 5min walk but were lazy) and i noticed the car shudders when i start the engine and turn it off, also the turbo is now making a winey noise, should i stop driving this bad boy?

i thought google was built on dogpile.com?
uh oh whining turbo noise isnt good
that "uh oh" shounds expensive :)

I started the car today drove to the top of the road whining noise still there so i didnt take it to work, shall i still go ahead with this pressure test or do i now have bigger fish to fry?
maybe it wasnt a boot leak , just your turbo unable to generate enough boost!

time for an upgrade then....;)
I think you'll find this is the problem.

Check the rod on the wastegate for a partially seized rod. Test with a vacuum pump and make sure it moves form one end stop to another. The rod can sometimes be freed off by lubricating but will probably require a new one if unsuccessful.
ok, so ive done the pressure test anyway to see if there is any air leaks, but that came back all good, the turbo on this is a GT1749V not VNT style turbo, I cant seem to find the actuator rod thing, shall I just go ahead and change the turbo? maybe hybrid??
yeah sorry for late reply, I was gonna suggest wastegate issue as everything else seems ok, but whining turbo noise has always to me meant issues on turbo, I'm not a mechanic but AS has taught us all few things huh guys

I wouldnt go swap turbo completely, test it or get tested 1st as its expensive, then you can be sure its this or not & as Mach said could be rod
hmm when you say wastegate do you mean the solenoid block? i had the turbo checked and the guy said it seems to be fine, i read on another forum that it could be the egr valve, some guy had the same issue on an a6 2.0tdi didnt come on up as anything on diag turned out to be egr,do you guys think that would be looking into, its around £50 for the valve so would be the next cheapest thing i guess

this is starting to do my nut, im going back to petrol after this! I wonder if Audi would give me a straight swap for an R8...... :)
Remember the wastegate is controlled by vacuum on this car. You say 'pressure check' but was the guy checking it right? There is a union in the pipe just behind/above the rear the boost pipe at the back of the engine on the left hand side as you are looking at it. This can be separated there and tested from this point. If you can't get under the car to observe the rod try to use a mirror to see it behind the engine. Unlikly that it is but before replacing the EGR check measured value block 3 and look to see if the specified and actual readings roughly match. You can basic set via this channel too so it will be easy to check. The duty cycle can also be read here. Remember that if idling for over a few minutes the ECU will switch the EGR off so don't get confused if the readings suddenly change drastically. A quick blip of the throttle starts the sequence again. As for the turbo noise, when it gets to this point its game over anyway. The turbo comes with the manifold as one piece and is quite easy to replace. They are common faults and I'd like to make a point that I had one blow up the other week whilst it was having an MOT, so rev it up at your own risk.
schweeet, guys can anyone recommend a good garage to take this to, the local ones around here are generally muppets, im in south bucks, anywhere in london or the a40 stretch to london would be fine (uxbridge, ruislip etc.) Berkshire area is also fine slough reading windsor etc.
Hay everyone

Managed to get this fixed, turned out to be the manifold flip motor part number A038128063L

running smooth now :) thanks all for your help
What's the manifold flip motor? Where does it fit and what does it do?
manifold flap - its a motorized flap in the inlet manifold that blocks/limits incoming air - rather like a petrol cars throttle valve, but it doesnt control the engine by controlling air flow, just shuts off the airflow to help a smooth shut down among other things - if its not opening properly then the car might not make boost cos theres an obstruction in the inlet pipe - hence the underboost code.
Hi all, I've got the same issue as the OP. A4 170 tdi. Brd engine. Turbo makes more of a groan than a whistle. I'm pretty crap with self maintenance so can anyone recommend someone around south Leicester that could scan it etc?

Cheers in advance

Thanks mate. I was going to take it for a scan but the problem appears to have manifested itself as a blown turbo. Plumes of white smoke started initially just when cold but now all the time. Not much of a drop in performance but I'm guessing it's been on its way out for a while. Absolutely gutted. It's only done 52k ***
Hey guys I know this is a real old post but did anyone sort their limp mode issue out and if so what was it?!?!

I'm having the limp mode issue myself! :(