Code P0299 "turbo underboost" Resolution Repository

TheProspector

Member
Joined
Aug 8, 2012
Location
New Mexico
TDI
05 Passat GLS TDI?
Sorry in advance for the long-winded post, but I need help on my BHW Passat with 245k miles.

I live in the foothills outside of Denver for about 4 months and climb about 1300ft in elevation in about 11 miles on my commute home. About 6 weeks ago my car went into limp mode and gave the p2099 code. I pulled over and found a vacuum line disconnected from the N75 valve. I reconnected the hose, cleared the code and the car ran fine for the rest of that night and the next day until the late afternoon when I was in a little of traffic and limp mode happened again. This time i was pouring white smoke out the back of the car. I pulled over and found that my turbo was broken. Over the next two weeks i changed the turbo(I cheaped out and ordered the cartridge to save money) which went well but I was still constantly getting the P0299 underboost code. So i changed the N75 valve which helped it go from a constant code to an intermittent one. Finally, I checked the adjustment of the actuator stop and rod and found out it was out of adjustment. After adjusting the stop, the car ran fine for about 3 weeks. I took in on a 12 hour round trip drive and had a overboost code once but that was it. Three days ago i started getting the p0299 underboost code anytime i even barely asked anything of the engine. To avoid the code, I was leaving the car in 4th gear to climb hills. Yesterday, trying to merge into traffic, the car lost power again and was pouring white smoke and ate a bunch of oil meaning the turbo probably died again. I found a chaffed wire that I think maybe my underboost issue but my question is if you guys think the underboost code is causing my turbos to break or is it just an unfortunate coincidence of an old part finally breaking along with maybe a ordering a bad part and that breaking? Thank you guys for any help. It's much appreciated.
 

ciz51

New member
Joined
Oct 30, 2007
Location
Cobb Island, Maryland
TDI
'04 Passat, 06 Jetta
On Passat TDI, PD, the Turbo, with No Vacuum, is at zero boost; To Quote martin1810passatsubscriber:

“With a VNT TURBO system you do not dump the air pressure (a/k/a "waste gate" .ed), you dump the vacuum. The vacuum is a very small thing so fine control is easy and lag is much reduced.
So, at start you have 100% vacuum and maximum vanes in turbo so maximum boost.

As engine rpm rise the boost reaches its maximum set point, the actuator % starts to reduce. This reduction in actuator % moves the vanes that direct the exhaust gas onto the turbo impeller. So the actuator % is going down but the boost stays at full.

The actuator % drops because it is venting vacuum (not air). This venting of vacuum gives very fine control of the turbo vanes which gives fine control of the boost pressure. At rest, the turbo vanes are in the max boost position so if they stick, they stick at full boost. So now, even if the actuator vents vacuum and the actuator % drops, the boost stays stuck at full. Most systems are designed for full boost at about 1500 rpm so now when the engine rpm goes higher the stuck vanes allow the boost to rise higher than maximum.

This is not good and the engine drops not limp mode. So constant overboost with a VNT is nearly always turbo vanes sticking and a constant underboost is nearly always a vacuum leak.”
 

deckerfl

Well-known member
Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
I'd like to chime in on this post.
2004 Passat TDI, 150K Miles, Rocket Chip stage 2
I've had the dreaded underboost error, and the MAF error. changed MAF, Pressure sensor, but in the end, my issue was boost leak. My boost leak was in multiple places. One was a slightly split charge hose, the "S" hose right after the turbo. Replaced that. it got better but still sometimes went into limp mode. Then changes all of the charge hose spring clips, including the one right on the turbo outlet. This one was worn and allowing the "S" charge hose to be pushed out a little, but this was not the real issue. this is the second time I've replaced the "S" charge hose. first time was the cable wear, next time, it split. I'm not replacing the "S" hose a third time, so for the future, I now have After market pieces to replace it, with Ebay piece, like Passat owners use to upgrade to the BV43A turbo.
I finally made a boost leak tester out of a Plastic water bottle (I'll try to post a pic later) and found my new leak. It was in the 90 degree Charge Hose right before the "Throttle" Actuator. I thought I had checked that Charge Hose, but the split was way underneath and I missed it. I replaced that and my Under Boost Codes are gone. :) , I also did other tests in this thread, checked turbo actuator, vacuum lines, applied vacuum to actuator to make sure it was actuating, and added support to where vacuum line meets actuator like previous posters...
Very useful thread, thanks to all the contributors...
 
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boobap

Member
Joined
Apr 26, 2016
Location
fallon, NV
TDI
BHW
I got the dreaded p0299 code the other day... Wife and I were on a road trip (about 500 miles into it) when wife called me and told me to stop on the side of the freeway because the car has no power. I've gotten it towed back home (very long story) and haven't had time to inspect it. Here is the "setup":

We were driving up a very slight grade just before Baker City, OR at 75. It was about 95 degrees out when she hear a "pop" (she compared it to the sound of running over a cheap water bottle) then it lost power. I'm fairly mechanically inclined, but like I said I haven't had time to inspect it yet and just wanted y'alls input on where to start.

Her saying that it sounded like "pop" leads me to believe it is a boost line that separated. I took the top cover off of the engine to inspect the boost lines on top because I had taken them off to replace the dreaded coolant flange and TD pump gasket.

Any and all input would be great. I will dig into it this weekend and let you know what I find...
 

Windex

Top Post Dawg
Joined
Apr 1, 2006
Location
Cambridge
TDI
05 B5V 01E FRF
My first places to look would be at the elbow right before the intake/anti-shudder valve, and if that's intact, I would check the s-shaped hose right off the turbo to the cross-tube under the radiator.
 

truman

Top Post Dawg
Joined
May 18, 2000
Location
columbia,MO,usa
TDI
'05 Passat Variant, Still miss the 03JW
After replacing a couple of boost hoses, with significant improvement, the N75 was replaced and that essentially resolved limp mode issues. In the last 6 months, I have had 1 limp mode, which surprised me. Non since that 1 instance. Since N75, turbo response is much better and smoke at WOT is way down. Boost leaks and N75 get my vote.
 

boobap

Member
Joined
Apr 26, 2016
Location
fallon, NV
TDI
BHW
As suspected, the lower passenger side boost line popped off the metal tube. It was a "self induced" situation. 3 months ago I deleted the BSM and didn't put the lock back where it should be. So it's been my DD for the last 3 months and it decided to pop out while we were in the middle of nowhere land...point is, always do some good QA before calling a job finished. And don't drink to much while doing these jobs! HAHAHA
 

atikovi

Veteran Member
Joined
Jun 22, 2002
Location
Suburban Washington DC
Just found this thread on a search. Have an 06 Jetta BRM and just had the turbo rebuilt. After installing it the car runs like crap. No power until 2200 rpm, lots of black smoke, P0299 code. If I remove the hose from the VNT actuator it's a whole different animal. Tons of smooth power, no significant smoke. I assume removing the hose keeps the turbo vanes closed so it builds full boost all the time. Ran some tests. Put vacuum to the actuator and the rod moves smoothly and holds vacuum. Checked the N75 solenoid and it puts out good vacuum to the valve. MAF sensor is new. What else can I check?
 

atikovi

Veteran Member
Joined
Jun 22, 2002
Location
Suburban Washington DC
Pulling the hose from the actuator will open the vanes fully. BRM's have a problem with the vanes being driven too far closed due to wear in the vane unison ring. This does not allow a sufficient volume of gas through the turbo and causes huge backpressure in the manifold. Once you get over the hump and the turbo finally spools up, the car will run OK. You just need to adjust the vane control lever stop screw. There are several threads about the problem search "BRM stop screw adjustment".
I've already done the MB 11 charge pressure control test and it showed 960 to 1050. Within the 80-250 acceptable range. Wouldn't that indicate the stop screw is in the correct position?
 

concours

Veteran Member
Joined
Jul 4, 2001
Location
Kensington, NH
TDI
2006.6 Jetta GLS 5 speed 125,000 miles, 2001.5 Jetta GLS 5-speed, Tornado Red, Monsoon w/CD changer
My P0299 is accompanied by what I think is clogged intake, or EGR or Anti-shudder valve.
 

Gnant

New member
Joined
Jul 27, 2019
Location
Scottsdale AZ
TDI
2005 Jetta Wagon
Sorry to bring the infamous P0299 code back to the top. But after much reading, and much work, I can't seem to get this code cleared up. It is a 2005 Passat 2.0 TDI with 110,00 miles. Immaculate shape so it is well work getting road worth.

What has been done so far.

1) new turbo and N75 valve done at a shop as they said that is what it was. Code was still present.

Car then sat for two years out of frustration. In the last 10 days I have done the following.

2) all new vacuum lines and routing is confirmed as correct. All held vacuum including the reservoir.
3) new vacuum pump as it was leaking at the port to the check valve for the brakes.
4) vacuum tested the N75 and it was operating smoothly
5) removed all inter-cooler hoses and inspected. All solid shape.
6) replaced EGR as it had clearly been stuck for a while and the motor was burned out.
7) inspected butterfly valve next to EGR and was clean.
8) installed new waste gate solenoid as it was leaking.
9) pulled top and bottom metal hoses for the turbo and replaced metal gaskets. Hoses were fine.
10) for giggles put in a new boost sensor. That was a waste.
11) confirmed clean airbox and new filter.
12) replaced fuel filter and now have 13 PSI

The car has way more power and the code now appears as a soft code usually unless I stand on it. The thing is I have turbo for about a minute, no matter how I drive it then the computer is kicking it off. I can clear the code while driving and she scoots, but for a minute. I can also turn on and off the key (yes while going down the road), and again, turbo works great, but for a minute.

I would like to Ohm test the MAF sensor but can't seem to find specs if anyone could help me out. I am also highly suspicious of the gas pedal because if I floor it softly, I don't get the turbo response I do if I stomp on it quickly. I mean smash it.

Related to the gas pedal, what I would like to confirm is that my throttle position sensor reading is stuck on 95.3. From my reading that is the butterfly valve next to the turbo and it is supposed to be full open and only closes when the car is shut off to stop the engine from a run-on condition. Do I have that understanding correct?

Also, is there way to test the inter-cooler beyond a smoke test? Any help is appreciated. This place has been very helpful and I have read as much as I could but I am stuck at this point.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
I have had O-ring leaks that were not apparent from visual inspection or while the engine was running. I made a cap for the turbo inlet and a fitting to go over the hose end that clips into the anti-shudder valve. The latter had an air hose fitting. I set my air regulator to 10 psi and kept air flowing until I could hear and feel where it was coming out.
You are correct on the butterfly (anti-shudder) valve operation. I believe the TPS is actually a pedal position sensor.
 

Gnant

New member
Joined
Jul 27, 2019
Location
Scottsdale AZ
TDI
2005 Jetta Wagon
I have had O-ring leaks that were not apparent from visual inspection or while the engine was running. I made a cap for the turbo inlet and a fitting to go over the hose end that clips into the anti-shudder valve. The latter had an air hose fitting. I set my air regulator to 10 psi and kept air flowing until I could hear and feel where it was coming out.
You are correct on the butterfly (anti-shudder) valve operation. I believe the TPS is actually a pedal position sensor.
For the price of O-Rings, I think the thing to do is just replace them. Thanks for the suggestion as they all did look good visually. I like your suggestion for testing the inter-cooler itself. So if the O-rings aren't it, I will make a similar setup.
 

N2OKX

Well-known member
Joined
May 22, 2005
Location
Kentucky, Western
TDI
looking
9 hours later on P0299 turbo underboost

I was working a 2005 Passat TDI with 246,000 miles. Presented with the infamous P0299 code plus P0741 (torque converter!). Since the owner admitted he had run off the road (front grill inserts missing), I started with the turbo hoses/ducting, but only a visual inspection. Later, I did a pressurized smoke test. All okay.
Of course, I checked the movement of the turbo wastegate actuator rod by pulling vacuum and measured the vacuum near the tandem pump. Again, all good.
Finally, I pulled the N75, Wastegate bypass regulator valve and checked it. It was not holding a perfect vacuum, so I replaced the valve, thinking that I finally isolated the problem. In retrospect, the problem was the opposite of what the DTC indicated. I should have been looking for a vacuum leak.
During all this, I reviewed most of the posts in this extensive thread. By the way, very few solutions were posted. Folks, please follow-up with what fixed the car. Maybe that is hard to do for this code, since there are multiple causes and they are very hard to find with absolute certainty.
I thought I had already checked all the vacuum hoses, but this morning after concluding there had to be a vacuum leak, I finally got breakthrough! I ended up pulling a vacuum on each section of hose until I found the culprit. It was the hose from the "out" nipple to the turbo. At first I suspected the rubber el, but after pulling it off and checking just the hose, I found that the hose did not hold vacuum. The hose looked perfectly okay. It was only after very close inspection that I found a slit near where the hose connects to the rubber el. On a Passat, this N75 valve is buried deep and the hoses no not lend themselves to visual inspection.
The mistake that I made the first time I checked the hoses was in pulling the vacuum with the key off. I was only checking for vacuum from the check valve to the N-75 valve. I was not checking all the way to the turbo. With the key on, I would have seen the leak, since this opens the N75 valve. Hind sight is perfect!
Hate to admit to a novice mistake, but it happens. I doubt that I will ever forget it either. I hope this helps someone. Whenever I use this site, I try to contribute a post as payment for the help that I have received. TDI club is without a doubt, the best site out there. (That is not intended to be a slam on the others, just my opinion.)
 

Baumjaeger

Member
Joined
Feb 3, 2015
Location
Vancouver Island
TDI
2005 passat tdi
Ok I had this issue vexing me for ages and as I had purchased the car with a new turbo I spent hours looking for vac and/or/boost leaks. Nothing. Farted about with EGR restrictor and block off plates. Nothing....limp mode would just keep coming back.
Got to where I was going to have a spare ecu reflashed and swap out engine harness.

Then a buddy with same car and same issues helped me make some sense.

The new turbo came from Mahle. So did his.

I swapped in my spare Garrett and while it’s only been a week and I know I am hailing the vw gremlins...I have not gone into limp mode.

If you folks that have replaced your turbos can chime in if they happen to be Mahle branded then that would be very interesting.
 

concours

Veteran Member
Joined
Jul 4, 2001
Location
Kensington, NH
TDI
2006.6 Jetta GLS 5 speed 125,000 miles, 2001.5 Jetta GLS 5-speed, Tornado Red, Monsoon w/CD changer
First intercooler hose to fail was the small 90 degree bend at the firewall, (190,000 miles)going into the anti-shudder/EGR/intake manifold.

Most recently, (230,000 miles) the discharge hose, right out of the turbo. Groove worn in it from adjacent cable, then burst when pulling a long hill. I had JUST completed camshaft & TB replacement. Totally coincidental, but added to urgent repairs, down time.
 

wrx603

Member
Joined
Jan 29, 2020
Location
maine
TDI
05 passat tdi
wish i had found this sooner. I'm battling the same code. I've smoke checked the intake and vac system, replaced the n75, watched the turbo actuator, pulled the turbo and cleaned it, all to no avail. ordered a new turbo the other day as a next step.
 

Tom in PT

Veteran Member
Joined
Jun 7, 2017
Location
Twilight Zone, WA State
TDI
2005 Passat sedan - SOLD; 2013 Passat DSG; both purchased new
Auntulna's thread and the great pics should be the first place to look when these codes show up, and really owners should inspect that hose and the cabling at every oil change so this hose failure never happens. What a great service to the community to post that. I am about to do an oil change and will give that area another look-see, so far so good for my '05.

http://forums.tdiclub.com/showthread.php?t=243942
 

1.9glstdi

Veteran Member
Joined
Jan 13, 2010
Location
J-vill,FL
TDI
2005 passat waggon BHW PD
I got the dang code, I noticed the car was a little sluggy also, so I checked my vacuum lines and replaced them all due to condition and a new N75 valve just for good measure. I also installed the egr block off I had sitting in my garage since I bought the car. I left the egr cooler due to rounded off allen heads and heater help in the winter when we go to the mountains. The egr looked pretty rough, I had to vacuum out large pieces of soot from the intake after removal. Result is no more code or limp mode, my stage 1 Malone tune is more responsive I can sqeel the tires from a stand still and much more passing power now where before it did not do that. Mpg's are up by 2 putting me at 33 mixed driving after a tank just filled up after mods.
 
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Cody.tdi

New member
Joined
Nov 2, 2020
Location
Erie PA
TDI
04 jetta tdi wagon
After hours of reading through threads and a lot of time on this specific thread I found my issue. I replaced all vaccum lines to no avail. Then went to fix an exhaust leak from the lower egr cooler hose from the cooler to the main fold. Replaced the hose and got tons of power back and as of yet no underboost code in site! Hope this helps someone.
 

fil46

New member
Joined
Aug 17, 2023
Location
Greece
TDI
Polo 1.2 tdi bluemotion 2013
Hello there.have fun and drive carefully.
Here goes the story:
I drive a vw polo 1.2tdi blumotion 2013,and here it goes..
Glow plug light came on..
1st fault n75 and changed with new one m&d. Car afer that run smooth.
Next day glow plug again..
2nd fault wastegate and change it with new one. Car after that run smooth.
Next day glow plug again..
3rd fault MAF and changed with new one BOSCH.Car after that run smooth.
Next day fault again and show n75 again.
The car staying in the carage for a week and have tutbo down and serviced.vacuum test fine.vcds fine.turbo came in its place and was fine like new.
Taking the car and next day glow plug light again.
Other carage found timing belt untimed by one tooth.car in carage and timing belt newnext day guess what...
GLOW PLUG LIGHT AGAIN!!!!!!!!!!!!!
boost pressure control keeps poping up as a fault..
I have messure the n75 with a multimeter and i ve seen restinance between to pins 14 ohms and volts in plug from the car 8,9.same numbers with engine off and engine on.
Heeeeeeelp me!!!!

Thanks all in advance!!!
 
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