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Code P0299 "turbo underboost" Resolution Repository

SUNRG

Top Post Dawg
Joined
Oct 19, 2003
Location
Roanoke, VA
TDI
None currently. Previously owned 04 Golf TDI & 05 Passat GLS Wagon TDI
If you get a CEL / Emissions Workshop message, have the code read and it comes back with P0299 turbocharger underboost - please post what you did to resolve the problem to this thread.

This way anyone that gets this code in a B5.5 can view this thread and see what the most common causes and resolutions were.

Thanks!
 
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SUNRG

Top Post Dawg
Joined
Oct 19, 2003
Location
Roanoke, VA
TDI
None currently. Previously owned 04 Golf TDI & 05 Passat GLS Wagon TDI
*Update: reseating the loose line did not resolve the issue. Emissions Workshop (and I assume P0299) occured Friday again, coinciding with limp mode onset (driving up a slight incline at highway speed) stayed on until Sunday morning when the CEL went away, but my B5.5 went into limp mode three times during a round-trip drive from Roanoke, VA to Johnson City, TN.*

My B5.5 had increasingly been going into limp mode, eventually the CEL / emissions workshop light came on. P0299 was the code.

The apparent cause was a loose clean air line from the N75 valve to the air filter box. It was secure on the air box side but ready to fall off the fitting on the N75 side.

Reseating the line on the N75 valve seems to have resolved the issue. No cell or limp mode since. I will update this post if that changes.
 
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tpitt1946

Veteran Member
Joined
Jan 1, 2004
Location
Willits, Ca.
TDI
Jetta Wagon 2004 Silver
I've had to replace two N75 valves on my Passat. The most recent one was a week or so ago. I do see the new one is a little different. Hope it lasts.
 

texascadillac42

Veteran Member
Joined
Mar 14, 2007
Location
Decatur, IL
TDI
2000 Jetta
I am fighting this problem right now. I tried a spare N75 I had laying around with no luck. It wasn't a new one, but one I had from a spare motor so that's not to say it wasn't faulty as well. I checked all vacuum lines at the N75, checked that the turbo actuator was moving freely with vacuum applied and examined all intercooler hoses.

The car will run fine for several miles, whether its easy driving, or hard acceleration runs. Then all of the sudden (usually after pulling a slight hill at moderate throttle), it will go into limp mode. Code P0299 comes up as boost pressure control range not reached.

If I clear the code/shut the car off and restart it runs great for another couple miles. I am wondering if the MAP sensor is failing?
 

SUNRG

Top Post Dawg
Joined
Oct 19, 2003
Location
Roanoke, VA
TDI
None currently. Previously owned 04 Golf TDI & 05 Passat GLS Wagon TDI
sounds like you've eliminated quite a few possible causes. fwiw - Jeff (RocketChip) said excessive fuel or air filter restriction could trigger P0299.
 

texascadillac42

Veteran Member
Joined
Mar 14, 2007
Location
Decatur, IL
TDI
2000 Jetta
Checked the air filter last night, cleaned the snow screen out, and everything looked good there. Could be a fuel filter....

I noticed (and forgot to mention this earlier) that the car seems to surge slightly. Not enough to really affect speed, but you can feel it surge a little with moderate throttle input. Not sure if this is a common symptom or not.

I will put a new fuel filter on tonight or tomorrow. It has roughly 15,000 miles on it, but the car sat for a LONG time before I got it running again, so it may be time to change it again. I have no idea how old the fuel was in the tank, but several hundred gallons have been run through it since the fuel filter was installed.
 

texascadillac42

Veteran Member
Joined
Mar 14, 2007
Location
Decatur, IL
TDI
2000 Jetta
Well, after pulling the motor cover to change the fuel filter. I found the problem. I had checked all 3 intercooler hoses, but not the hose that connect the plastic tube at the back of the motor to the intake manifold. It had a nice split in the bottom of it.



Problem solved.
 

auntulna

Veteran Member
Joined
Mar 13, 2005
Location
Springfield, MO
TDI
05 GLS Passat wagon, mit panzer plate
Mine limps only once in a while when going uphill at 70+, otherwise it's very strong. This would be a maximum boost demand from the computer. Fuel and air filter are recent, so I don't think it's them. It never happened until I got RC2 13K ago.? I will check the hoses again, and then maybe buy a new N75? Hard to know if that would be it.
 

texascadillac42

Veteran Member
Joined
Mar 14, 2007
Location
Decatur, IL
TDI
2000 Jetta
It is worth checking all the vacuum lines going to the N75 with a tool such as a mity vac. That way you can see if everything is holding vacuum adequately, that the actuator arm moves freely through its range.... etc.
 

TheGrove

TDIClub Enthusiast, Veteran Member
Joined
May 17, 2006
Location
S Central PA (Breezewood)
TDI
2012 Passat SEL Premium Opera Red - Dieselgate Fix, KermaTDI Tune, 2004 Passat GLS Northern Green-RIP
texascadillac42 said:
Well, after pulling the motor cover to change the fuel filter. I found the problem. I had checked all 3 intercooler hoses, but not the hose that connect the plastic tube at the back of the motor to the intake manifold. It had a nice split in the bottom of it.



Problem solved.
That's the exact same place mine split! Glad you found it.
 

SUNRG

Top Post Dawg
Joined
Oct 19, 2003
Location
Roanoke, VA
TDI
None currently. Previously owned 04 Golf TDI & 05 Passat GLS Wagon TDI
*Update to post#2 above: Reseating the loose line (running from the airbox to the N75 valve) did not resolve the issue. Emissions Workshop (and I assume P0299) occured Friday again, coinciding with limp mode onset (driving up a slight incline at highway speed) stayed on until Sunday morning when the CEL went away, but my B5.5 went into limp mode three times during a Sunday round-trip drive from Roanoke, VA to Johnson City, TN.*
 

shri11

New member
Joined
Jan 14, 2010
Location
spring, texas
TDI
2004 Jetta TDI
P0299 Whistling sound

Hi all, drive a 2004 Jetta PD, I had been hearing a whistling sort of noise coming from near back bottom of the engine, almost near the exhaust pipe, and today check engine light came on, code P0299. "Faulty wastegate bypass regulator valve" one Probable cause was listed as "Faulty charge air pressure sensor"

Will any defect be visible by raising the car and looking under? thanks Shri Sarathy
 

TheGrove

TDIClub Enthusiast, Veteran Member
Joined
May 17, 2006
Location
S Central PA (Breezewood)
TDI
2012 Passat SEL Premium Opera Red - Dieselgate Fix, KermaTDI Tune, 2004 Passat GLS Northern Green-RIP
Probably, I believe one of the main culprits is the hose off of the turbo that rubs on a wiretie until it creates a hole.
 

auntulna

Veteran Member
Joined
Mar 13, 2005
Location
Springfield, MO
TDI
05 GLS Passat wagon, mit panzer plate
About The Grove's comment, my experience with a hole in the first hose off the turbo was low power all the time and smoke with acceleration. I think a true hole anywhere else along the charge air system will be felt as poor performance in multiple situations.

The underboost code is a lot harder to pin down, maybe N75, maybe vacuum leak, because the car runs fine most of the time. There is a procedure for a turbo boost test at myturbodiesel.com, that I would like to try when I can.
 

CharlieT

Veteran Member
Joined
Dec 10, 2008
Location
Houston, Tx
TDI
Audi TTqTDI, B4V, B5.5V, '12 NMS SEL
I got a P0299 for the first time today. It went into limp mode, but didn't set a CEL ?! I was amazed it went limp mode without a CEL ? nothing, no indication.
Cleared it, done another 40 miles since, runs fine, normal, lots of boost (RC1+) no codes ?
What gives ?
I am going to check all the boost hoses on Sunday, I had a good look today and nothing obvious. I moved the infamous rubbing wire from the hose under the turbo last year at 100k miles, so I don't think that is it ?
 

Mechnurse

Veteran Member
Joined
May 17, 2005
Location
Pahrump, Nevada
TDI
97/2K/05/15 Passat 06 Jetta TDI
I had this CEL many times. I had Jeff update my tune with the High Altitude tune and it still happened. Also check all your connections from the Turbo outlet hose to the intake manifold. If any seals are leaking it will be oily around them. I bought a new Turbo outlet hose and now no more P0299 issues. I wonder if it has to do with the restrictor in the outlet hose from the factory it is quite small compared to the updated hose.
 

TheGrove

TDIClub Enthusiast, Veteran Member
Joined
May 17, 2006
Location
S Central PA (Breezewood)
TDI
2012 Passat SEL Premium Opera Red - Dieselgate Fix, KermaTDI Tune, 2004 Passat GLS Northern Green-RIP
Welcome to the club! Mine does it from time to time I have finally chalked it up to the nature of the beast. Tends to do it more when I'm pulling long steady grades and the engine gets to a point where it wants to downshift. If I let it "slowly" downshift it will, on occasion, limp mode but if I push it a bit and force the downshift quicker it seems to do better.

Don't know that there is a real answer unfortunately.
 

CharlieT

Veteran Member
Joined
Dec 10, 2008
Location
Houston, Tx
TDI
Audi TTqTDI, B4V, B5.5V, '12 NMS SEL
Let me re-explain... I am not surprised by it going into limp mode, I have heard that does occur from time to time, especially with higher boost requests.

My surprise is that it set no CEL (and yes, my CEL light does work, checked that). And that it didn't clear with engine on/off/on.

It happened at a CRAPPY time, my wife had just left for a 3000 mile / 1 week trip. I had checked EVERYTHING with the car prior to her leaving, no codes in any of the controllers. She got about 300 miles and called me to say the car had no power. She described it as revs building, but car not going any faster. No CEL, and it did NOT clear after turning engine off/on twice. So I was fairly sure it was not limp mode and so I was left assuming that it was a torque converter issue.
Result was her turning around and me renting a u-haul dolly and heading ~150 miles to meet her. Plugged in VCDS expecting to find a transmission slip code, but nothing. Just P0299, which when cleared put the car immediately back to normal, wheel spinning RC1+ power.
End result, she was now too late to make her appt in NC, and so we ended up with a $600 flight and a $300 rental car. Not impressed... but I guess I should be happy I am not buying a new transmission/TC !

So... how do you clear limp mode without VCDS ? all I have read says engine on/off/on clears it, but that didn't work. I would like to not have to keep VCDS and laptop in her car to clear it !?
And I drove it, the limp mode was REALLY bad, no power at all, not really safe to drive on a Texas freeway !
 

TomB

Veteran Member
Joined
May 1, 2003
Location
Cle Elum, Washington/Las Vegas, Nevada
TDI
2015 Audi TDI Prestige Sport
Have you all had the EGR re-flash done that VW issue several years ago?

I had this issue regularly on the Passat with the older manufacturer date, and only 2 times on the other Passat.

After the reflash I have never gotten any more.

It definitely happened coming up a hill and the letting off slightly near the crest it would cause the issue. I could reproduce it regularly with the one Passat and not the other. After the re-flash there is a surge/hesitation but no CEL and no limp mode.
 

aja8888

Top Post Dawg
Joined
Dec 25, 2007
Location
Texas..RETIRED 12/31/17
TDI
Out of TDI's
Adding my two cents. When I had asked Jeff last May if his RC1+ recode covered the EGR recall and the glow plug voltage adjustment, he concured that it certainly did. Charlie just had the ECM upgraded to RC1+ by Jeff so I assume that he also is past the EGR recall flash by default.

To add, my Passat has never gone into limp mode since I have had it (~40,000 milres). Did I just jinx myself?:confused:
 

auntulna

Veteran Member
Joined
Mar 13, 2005
Location
Springfield, MO
TDI
05 GLS Passat wagon, mit panzer plate
Somewhere on one of the forums Jeff said his program was "MAF delete". Since I have RC2, I unplugged the MAF about 5 weeks ago and haven't had a limp since then. I have charged up the hills that would make it happen, and it's been fine. I don't know for sure if that is it, but if you have an RC tune, it's easy to try.
 

CharlieT

Veteran Member
Joined
Dec 10, 2008
Location
Houston, Tx
TDI
Audi TTqTDI, B4V, B5.5V, '12 NMS SEL
Well, I think I found my boost leak....



It didn't look bad until I started messing with it, but I will guess it has been leaking vacuum for a bit. Nothing showed up on logs that I had run, specified boost and actual boost tracked really well.

We will see if this helps. I replaced all the crappy braided lines with silicone, from N75 to vacuum tank, and N75 to actuator.
 

CharlieT

Veteran Member
Joined
Dec 10, 2008
Location
Houston, Tx
TDI
Audi TTqTDI, B4V, B5.5V, '12 NMS SEL
I just used some left over stuff from my silicone tubing upgrade on my B4.
I used the black, firm silicone, 3mm ID x 8mm OD (I think)

Pretty sure it is McMaster Carr Part # 5041k521

I was a pretty tight fit over some of the nipples, but that just means it isn't coming off anytime soon.
Seems to work fine.
 

rocketboy52

Veteran Member
Joined
Jan 13, 2010
Location
Tehachapi CA
TDI
2004 Passat TDI
I'm having the same problems that most of the previous posters have had, and this is my first real issue with my latest edition to my diesel family. My wife complained of the car not being able to go up hill. We bought the 04 passat in November with ~140k on her. When taxed slightly, she stops producing power, and rev's high without shifting. Using the VCDS, I get the following:
2 Faults Found:
16485 - Mass Air Flow Sensor (G70): Implausible Signal
P0101 - 000 - -
Freeze Frame:
RPM: 1218 /min
Torque: 0.0 Nm
Speed: 68.0 km/h
Temperature: 50.4°C
(no units): 15.6
(no units): 0.85
Temperature: 89.1°C

16683 - Boost Pressure Regulation: Control Range Not Reached
P0299 - 000 - -
Freeze Frame:
RPM: 2100 /min
Torque: 234.0 Nm
Speed: 110.0 km/h
Load: 52.5 %
Voltage: 13.22 V
Bin. Bits: 00001000
Absolute Pres.: 2091.0 mbar
Absolute Pres.: 1540.2 mbar
Since I'm new to the car, it sounds like I need to get the engine cover off and the belly pan off and look at the Turbo intake hose, and N75. I'm not sure what N75 is yet, but I'm guessing there is a schematic that everyone else knows about that explains what it is. From the previous discussion, it sounds like a vacuum actuated relay? Does anyone have VW part number for it? I really appreciate the others who posted the part numbers for the intake hose and new silicone hose to replace the braided hose. My Mercedes 300D used that fabric covered braided hose all over the place and I replaced it all with new Viton hose, only to have the viton fail on me a number of times in one year. I ended up buying MB original stock and figured if I got another 20 years out of it, I wasn't doing that bad!:cool:
 

TheGrove

TDIClub Enthusiast, Veteran Member
Joined
May 17, 2006
Location
S Central PA (Breezewood)
TDI
2012 Passat SEL Premium Opera Red - Dieselgate Fix, KermaTDI Tune, 2004 Passat GLS Northern Green-RIP
It may be the N75 but most likely it is a leak in one of the hoses between the turbo and the intake. There are 2 main places, one is down by the turbo where the hose rubs against a battery cable. The other is on top of the engine in the back where it meets the intake. Mine split at the back by the intake and gave the same codes as you are seeing.
 

rocketboy52

Veteran Member
Joined
Jan 13, 2010
Location
Tehachapi CA
TDI
2004 Passat TDI
TheGrove said:
It may be the N75 but most likely it is a leak in one of the hoses between the turbo and the intake. There are 2 main places, one is down by the turbo where the hose rubs against a battery cable. The other is on top of the engine in the back where it meets the intake. Mine split at the back by the intake and gave the same codes as you are seeing.
The hose on the top, making the 90º turn into the intake manifold, there was a .5 long split. Oil mist was all over the top of the engine valve cover that fanned out from the split, so it was pretty easy to identify once the engine cover was off.

I ordered from: https://www.1stvwparts.com/catalogs.html
for some reason if you search for part #: 3B0 145 838A you won't find it, if you take out the spaces and search for: 3B0145838A you'll get a hit. $95 vs $125 at world impex.
 
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