16618 - Boost Pressure Regulation

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Going up a mountain and floored the accelerator to try to pass a vehicle, the car went into limp mode. Coasted and pulled over, shut down the engine for a few secs, then started engine and went off my merry way without any other mishaps.

Plugged in the VCDS and it reported this...

1 Fault Found:
16618 - Boost Pressure Regulation
P0234 - 000 - Limit Exceeded (Overboost Condition)
Freeze Frame:
RPM: 2142 /min
Torque: 336.0 Nm
Speed: 112.0 km/h
Load: 83.1 %
Voltage: 13.38 V
Bin. Bits: 00101000
Absolute Pres.: 2305.2 mbar
Absolute Pres.: 2590.8 mbar
So the list items to check. VNT actuator movement, N75 (have to read up on how to check it, any leads?) and vacuum lines.. Any other items I am missing?

One thing I am happy with... At least my engine is putting out the advertised 247 ft/lbs of torque with the stock ECM flash. :cool:



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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
My $.02 worth, if this is the only time it has done it chalk it up to a fluke and drive-more / worry-less. The 2004/2005 Passats have a habit of going into limp mode, I found mine used to do it most often when floored on a hill as well. I would say mine did it every 2-3 months out of the blue. I got pretty good about cycling the ignition while coasting down the highway instead of pulling over.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Thanks for chiming in. Yes, this is the first time it has done this. I've been driving car around in flat land and it has been acting fine. I even had to floor it when I inadvertently turned in front of an on coming car. Luckily it didn't do it.

But interesting tidbit on your cycling of the ignition. You would shut down in neutral while the car was rolling and restart the car?


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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
Yes, pop into neutral turn the key back 1 click to off then start it back up.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
I had a revisit of this same issue a few days ago while driving up a long mountain grade causing a heavy load on the engine.

The last go around, I pretty much didn't do anything except an Italian Tuneup and the code never came back. Since then, I had a 16683 code 21,000 miles ago in Aug 2017 and replaced the N75 valve along with several of the cloth covered vacuum lines.

Upon researching again this issue, someone reported that the dealership replaced the MAF to fix this on their Passat. Can the MAF really cause 16618 or is the dealership blindly throwing parts at it and it was just a fluke as TheGrove previously mentioned?

However, I did find my snow screen clogged and yanked it out. All vacuum hoses and charged air hoses look good. Drove around doing the Italian Tuneup and acting like a mad man with several cycles of WOT's. No codes came up during that process.

I hope that does it. Because I don't really want to pull the turbo to clean VNT, plus I have to get back to the mountains this weekend. Passat Wagons are very useful with it's cargo space. If I didn't need it, I would be taking another vehicle for the trip.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
Are you certain you don’t have a boost leak somewhere? In my experience the system will tolerate small leaks for quite a while until something puts it over the limit.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Thanks for the reply.

Visually the hoses look good and have a tight connection. I have a somewhat newer Factory turbo outlet hose and intake manifold elbow hose.

I really can't be sure if the connections are leaking just by revving the motor, it needs a load. I'll have to fabricate something where I can pressurize the system. Unless there is setup readily available or a process out there already that I don’t know of.

16618 is an overboost situation. Not sure if leaking hoses would cause that also. But leaking hoses can cause a 16683, P0299 - 000 - Control Range Not Reached which I had before on a blown hose.




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Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
I put a cap on the turbo inlet and cut an ABS fitting to go on the outlet end of the hose going into the anti shudder valve. I had to use a continuous low pressure air flow to find a leaking O ring. Which looked fine btw.
Overboost doesn't seem consistent with a leak but I have seen limp mode with no codes multiple times.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Update: Been a few months and I a have been up in the mountains a few times since and nothing happened. I am inclined to think the VNT got gunked up. Doing multiple Italian Tuneups exercised and freed up the VNT's movement.

I guess I'll have to WOT it more often.
 

Matt-98AHU

Loose Nut Behind the Wheel Vendor
Joined
Apr 23, 2006
Location
Gresham, OR
TDI
2001 Golf TDI, 2005 Passat wagon, 2004 Touareg V10.
On cars driven more highway than anything, I rarely see the vanes gunk up. On city driven cars? Yea, absolutely.

It's also pretty easy to visually confirm if the vanes are sticking or not if you have VCDS. Start the engine, login to the engine computer using VCDS, select "Basic Settings" and enter number 11 in the first field, hit "Go!" Then hit the "On/Off/Next" button at the top. The engine RPM will rise and the computer will every several seconds change the N75 from fully on to fully off.

While it's doing this, you can watch the turbo actuator cycle and get a visual on if it's moving smoothly and rapidly, or if it hangs up, even for just a split second, at some point. If it's slow releasing, but doesn't appear to hang up, it could be a lazy N75 or obstructed or kinked hose on the relief side of the circuit (set of hoses that go to the small port on the air box). If you question the vacuum output from the N75, attach a vacuum gauge to the hose going to the actuator while running the same basic setting 11 test and see how it operates. Pay particular close attention to how rapid the vacuum gets released when the computer switches the N75 to "off". It should be nearly instant drop back to 0.

If it appears fine, then go ahead and apply vacuum using a hand vacuum pump with a gauge to the actuator. Most of the BHW turbos tend to take about 17" mg to bring the arm to the stop screw. That's a bit less than what the BEW/ALH turbos require (closer to 18.5").

If that checks out as well, and once again you don't notice any hanging up while actuating it manually, in all likelihood you simply have a flat worn out control ring and lever for the vane mechanism inside the turbo. This is actually quite common and once you've exhausted the other possibilities as described above, by process of elimination that's almost certainly what's going on, and the only assured fix is to put a NEW OE/Garrett turbo on.

It's better than playing the guessing game. Heck, I've had some people "clean" the turbo vanes, only to have the overboost return after a number of weeks anyway. So even if you do notice sticking vanes, if you'd rather have an assured long-term fix, it's still better to simply put a new Garrett turbo on. I've had some cars that were more city driven where they had unfixable overboost (until the turbo was replaced with new) with only 100,000 miles on them. Some go 300,000 without issue. Depends a great deal on the driving conditions it normally endures. The more inconsistent the throttle (i.e. frequent stop and go driving) the more the vane mechanism has to move through its full range of motion and the more wear is going to happen between the control ring and lever. They don't last forever, that's for sure.
 

50harleyrider

Top Post Dawg
Joined
Jun 16, 2007
Location
charleston,wv
TDI
2005 B5.5 TDI/geared BSM, BV43A turbo,stage 2 TDTUNING. 2005 5sp manual passat tdi stage 2 tdtuning,BSM delete. 2015 Passat TDI 6sp manual.
the little 90 at the top of the engine will leak boost and cause that to happen. Take it off and look at it closely. It doesn't readily show leakage. I've been driving these cars for years and never had one go limp other than the boost circuit leak and when I needed a tweak in a stage 2 tdtuning tune when I put a BV43A on one.
 

DeliveryValve

Veteran Member
Joined
Mar 27, 2007
Location
Western US
TDI
Passat GLS Wagon
Great Information Matt. Yes this car is mostly driven around town. Not a lot of highway driving. When I get a chance I'll dig in more, but it's been running fine as of late.

@50', I mentioned above that I replaced that elbow hose not too long ago. On re-exterminating it, it still looks goods.
 

Matt-98AHU

Loose Nut Behind the Wheel Vendor
Joined
Apr 23, 2006
Location
Gresham, OR
TDI
2001 Golf TDI, 2005 Passat wagon, 2004 Touareg V10.
Great Information Matt. Yes this car is mostly driven around town. Not a lot of highway driving. When I get a chance I'll dig in more, but it's been running fine as of late.

@50', I mentioned above that I replaced that elbow hose not too long ago. On re-exterminating it, it still looks goods.
When it's a boost leak, you'll know. They smoke a LOT when there's a leak, largely because the MAF is still reporting the full volume of air, and thus the ECU responds in kind by commanding all the fueling from the injectors when you're hard on it, but since a lot of air is escaping, it smokes a ton.

Besides, when it's a boost leak, chances are good it will be an underboost code rather than overboost (this is mostly directed to 50harleyrider).

Overboost code and little to no smoke, one can pretty easily rule out a boost leak as being causal.
 

50harleyrider

Top Post Dawg
Joined
Jun 16, 2007
Location
charleston,wv
TDI
2005 B5.5 TDI/geared BSM, BV43A turbo,stage 2 TDTUNING. 2005 5sp manual passat tdi stage 2 tdtuning,BSM delete. 2015 Passat TDI 6sp manual.
Yep, Most likely a dirty vnt mechanism causing overboost. I would suggest checking travel of the actuator arm with you mighty vac. You may require a good 'Easy Off' cleaning or turbo removal and inpection and cleaning of the vnt mechanism. There are several good threads on here and compared to an ALH, the BHW turbo is an easy removal.
 
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