Passat B5.5 Recurrent Limp Mode Defies Repairs and Frustrates Both Owner and Mechanic

[sdcatdi]

My 2005 B5.5 Passat with about 135K on the odometer recently began going into limp mode sporadically. Took it to my local independent mechanic and the saga of attempting to solve the problem began. Codes were scanned, vacuum system and fuel system issues were ruled out. The turbo was chemically cleaned. Drove away and within 30 miles had limp mode again.

Turbo was then removed and replaced. Picked up the car and within 50 miles limp mode returned. Back to the shop multiple times for trial-and-error recalibrations of the turbo (shop informed me the turbo came from the manufacturer mis-calibrated). Shop would test-drive the car, pronounce it fixed, then I'd drive away and limp mode would recur within a day or two, and we'd start again.

Finally the new turbo was replaced under warranty and the shop drove the car about 60 miles without issue. I picked up the car and within 100 miles intermittent limp mode returned.
While not always the case, the problem typically occurs when the engine is cold and/or when I'm going up a hill. I then pull off the road/freeway, restart the car, and things are fine until the problem recurs - sometimes within minutes, sometimes not for days.

I'm at the end of my rope and I think my mechanic is too. I've changed the fuel filter, air filter, fuel pump, turbo. I'm now over $2,500 into this problem and still experiencing the same issues that prompted the first visit.
Has anyone experienced this problem before? Any idea what the cause may be or what else can be done at this point to address it? I'd very much appreciate any guidance the group can provide on this. Thank you!

 

[scoobysmak]

I know almost nothing about TDI's but almost sounds like a bad electrical connection of sorts, any loose ground or sensor wires be a problem. Maybe the ECU? Just blind guesses from an armchair mechanic.

 

[1854sailor]

What codes are showing up? Could be something as simple as a boost leak. Have you or your mechanic done a VCDS log of boost requested vs. actual? Have you checked the operation of the N75 Valve?

 

[Windex]

Have you replaced the n75 valve?

Do you have a boost gauge?

 

[sdcatdi]

Thank you for the replies.

I know the mechanic did boost tests and, while the old turbo was not making boost, the replacement is.

I'll definitely check on the N75 valve. I'll also check on the codes.

The issue is intermittent, sometimes accompanied by CEL (but not always, and it disappears on its own), or by an "EMISSIONS WORKSHOP!" alert.

 

[s4phillips]

What I am going to ask is antidotal in nature, with no facts or data...

What version of code is loaded in the ECU? When we first got our used Passat with 93,000 miles it did exactly what you discribe a few times when cold and climbing a hill. Since that time the ECU has been refllashed by the VW dealer for two different updates and it never did that again. I never did find a cause, unless I accidentally fixed it while doing another job (like the geared balance shaft module) and never noticed anything wrong on disassembly. I assumed our fix was in the updated ECU software.

 

[owr084]

When you say the codes were scanned, with what? A VCDS cable or a generic obd ii cable. if the latter, find someone scan it with a VCDS cable. If the former, post a printout of the codes.

 

[Matt-98AHU]

Well, I guess we would need to start with what codes are being stored when it does go into limp mode?

Is the turbo providing TOO much boost? Or not enough? Depending on which it is will determine the diagnostic path to take.

Seeing as how it's a new turbo, I would have my doubts that it is overboost unless the N75 is at fault (which is honestly kind of rare on vacuum controlled systems I find... The old wastegate turbo TDIs, on the other hand... might as well replace those every few years on some of those). But it's easy enough to check with a vacuum gauge and the right scan tool.

If the hose that goes between the N75 and the air box is kinked, that can certainly cause an overboost as well. That is where the vacuum that was applied to the actuator gets relieved to when the computer requests a reduction in boost. If that vacuum cannot escape to the air box, the actuator stays applied and it overboosts.

If you have an UNDERBOOST condition, you either have a large boost leak somewhere, which should be pretty obvious and likely audible/leaves a trail of oil, or you have a vacuum leak (and remember, diesels do not have manifold vacuum...). Also easy enough to check. I've seen a couple different hoses on BHWs have leaks, like the turbo outlet hose. I've also seen the elbow that goes into the intake manifold split. I've also had vacuum leaks from various lines and even had a couple where the nipple on the tandem pump was the source of the vacuum leak and caused underboost before.

Also, I have seen some TDIs crack EGR pipes and cause underboost as well. Can't say that I've seen that happen on a BHW yet, though... But certainly a leak of exhaust pressure pre-turbo means you have less exhaust energy to drive the turbo, and thus you will not have the boost response or max boost that the computer is requesting.

Having the right scantool and a vacuum gauge helps a LOT.

Or, you could make a very long trip to Northern California and I'd be happy to take some time to do some diagnostics.

 

[Windex]

My B5.5 had a bad N75 cause an intermittent limp prior to replacement a couple years back.

 

[aja8888]

Mine (2005 Passat B5.5) did the same and it was a split in a large diameter 90 degree hose that was not visible until you took off the hose and squeezed it.

 

[turtle1026]

I have said this a few times before and experienced it myself. I believe this is usually vacuum related. My limp mode was cured after I replaced this vacuum hose that comes off the tandem pump. The bad news is that the hose broke and I had the joy of driving home in limp mode and without power brakes. The good news is that I found the cure to my limp mode. Any auto parts store will have this hose by the foot. It will cost you $2 and is worth trying it. Even if it is not visibly cracked it can be leaking vacuum through cracks.

 

[Brian's96TDIPASSAT]

Can't help ya much without a code, underboost, overboost?

 

[tpitt1946]

I would go with the N75 valve. I've changed several on my Passat and carry a spare with me at all times. I've become an expert at changing them. I don't know why I've had so many problems with them. I've checked every line and connection out. Frustrating.

 

[deming]

How about a couple good pictures of exactly where the N75 valve and
this 90 degree vacuum hose are located ?

I have never replaced either one, but with two 05 Passat Wagons sitting in storage; I better know exactly where they are located and I had better keep a spare N75 valve on the parts shelf.

 

[go2toa]

I have an 06 and it goes into limp on hills every day. Then I plugged a laptop + obd-ii connector. It strongly resists going into limp mode when it's reporting to the laptop. It takes 50% more load in the cold early morning, and in the afternoon, I can't get it to go limp unless I unplug the diagnostics. Disconnected maf makes it worse. To me this sounds like a screwed up computer...that reflash mentioned earlier sounds interesting. My vacuum lines seem like great condition. Turbo also. N75 not sure.

BTW it's a ScanMaster with ELM327 IIRC. Stored error code is underboost turbo.

 

[go2toa]

I have an 06 and it goes into limp on hills every day. Then I plugged a laptop + obd-ii connector. It strongly resists going into limp mode when it's reporting to the laptop. It takes 50% more load in the cold early morning, and in the afternoon, I can't get it to go limp unless I unplug the diagnostics. Disconnected maf makes it worse. To me this sounds like a screwed up computer...that reflash mentioned earlier sounds interesting. My vacuum lines seem like great condition. Turbo also. N75 not sure.

BTW it's a ScanMaster with ELM327 IIRC. Stored error code is underboost turbo.

I guess all VWs are programmed to behave differently when they're hooked up for analysis. Note, this is pre diesel gate model year, but maybe they were practicing.

 

[Brian's96TDIPASSAT]

You guys all have mentioned "limp mode" but you haven't given a code that's set. Underboost?? Overboost?? You shouldn't start assuming anything until you know at the very least if it's over or under. Once you establish that, then you might stand a chance with figuring it out

 

[truman]

MIne goes into limp mode about once every mo to 6 weeks and it never trips a code.
About a yr ago, it was happening more frequently and my guru found a 1/2" split in the boost hose. At that time, it did trip p2099, I think it was, a couple of times- but rarely.

 

[1854sailor]

MIne goes into limp mode about once every mo to 6 weeks and it never trips a code.
About a yr ago, it was happening more frequently and my guru found a 1/2" split in the boost hose. At that time, it did trip p2099, I think it was, a couple of times- but rarely.

Are you certain of that? I believe that the ECU will set a code even if the CEL does not come on. Mine does. Are you using VCDS?

 

[Windex]

There isn't a TDI made yet that will go into limp mode without setting a code.

A code can set which cannot be seen by an OBDII scanner, only by VCDS, but a code will set.

 

[truman]

You are probably right about that. I have an old vagcom that doesn't work anymore. I use scan gauge to check for codes and it shows none.
My guru can check it in a few days when it goes in for its third driver side CV joint replacement.

 

[sdcatdi]

Re-Scan Tomorrow

I appreciate all the replies. Spoke with the mechanic at length a few days ago. The N75 was checked - no issue. The exhaust was checked - no issue. All hoses checked and vacuum tested - no issue, no leaks. MAF checked - no issue. Fuel pump and filter changed - no effect. Air filter changed - no effect. New turbo installed. Car hauls ass until it limps. The only trend is that it typically occurs when the engine has not yet fully warmed up, and when going uphill, and often when accelerating. Tomorrow it's back to the shop for another diagnostic - the first since the new turbo was installed. The shop is a VW/Audi specialist so I assume they are using an appropriate scanner. I'll get a full report and post results. I simply can't accept that no fix is possible, and pulling across 5 lanes of So Cal freeway to restart every few days is really getting old.

 

[1854sailor]

...The shop is a VW/Audi specialist so I assume they are using an appropriate scanner...

I have highlighted the key word there. IF they do have VCDS, see if they will run an "Auto Scan" for you. If they do, post the results here.

 

[sdcatdi]

Good advice 1854sailor - thanks. I'll definitely ask and will post results.

 

[Windex]

My N75 "checked out" fine when I was getting limp mode - replacement still solved it - they get lazy over time.

How exactly was it "checked"?

Also, the actuator for the turbo should start to move at about 4" vacuum and stop at 18" or so - was this checked on yours?

 

[tpitt1946]

My N75 "checked out" fine when I was getting limp mode - replacement still solved it - they get lazy over time.

How exactly was it "checked"?

Also, the actuator for the turbo should start to move at about 4" vacuum and stop at 18" or so - was this checked on yours?

I was going to say the same thing. I've taken to carrying a spare with me.

 

[sdcatdi]

VCDS Scan Result

Any assistance in interpreting this will be greatly appreciated:

Thursday,14,April,2016,09:28:31:17106
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8.1 x64
VCDS Version: 15.7.4.1 (x64)
Data version: 20160216
www.Ross-Tech.com

VIN: WVWAE63B25E054822 License Plate: TDI FULL SCAN
Mileage: 222340km-138155mi Repair Order:



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 3B (3B - VW Passat B5 (1997 > 2005))
Scan: 01 02 03 08 15 16 17 19 35 36 37 46 47 55 56 57 58 75 76 77


VIN: WVWAE63B25E054822 Mileage: 222340km-138155miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: 038-906-016-BHW.lbl
Part No SW: 038 997 016 T HW: 028 101 198 2
Component: R4 2,0L EDC G000AG 0314
Revision: 12345678 Serial number: VWZ7Z0D0380077
Coding: 0150034
Shop #: WSC 22136 444 04982
VCID: 2F6D7471BD5F9E46D7-5140

1 Fault Found:
16683 - Boost Pressure Regulation
P0299 - 000 - Control Range Not Reached - Intermittent
Freeze Frame:
RPM: 2142 /min
Torque: 210.0 Nm
Speed: 57.0 km/h
Load: 45.9 %
Voltage: 13.98 V
Bin. Bits: 00101000
Absolute Pres.: 2091.0 mbar
Absolute Pres.: 1652.4 mbar

Readiness: 0 1 0 0 0

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: 01V-927-156.lbl
Part No: 3B0 927 156 CF
Component: AG5 01V 2.0lPD USA 0404
Coding: 0001104
Shop #: WSC 05311 000 00000
VCID: 6CD7A37D4CC9255EB2-5140

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 4B0-614-517.lbl
Part No: 4B0 614 517 G
Component: ABS/ESP front 3428
Coding: 04257
Shop #: WSC 05311
VCID: 25419659BFA3D4162D-5140

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 6Q0-909-605-VW5.lbl
Part No: 1C0 909 605 C
Component: 09 AIRBAG VW61 04 0003
Coding: 12345
Shop #: WSC 05311
VCID: 24478B5DB4992D1E3A-5124

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel Labels: 1J0-907-487-A.lbl
Part No: 1J0 907 487 A
Component: Lenkradelektronik 0005
Coding: 00118
Shop #: WSC 05311
VCID: 2F6D7471ED5F9E46D7-5124

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 3B0-920-xx5-17.lbl
Part No: 3B0 920 929 C
Component: KOMBI+WEGFAHRSP VDO V07
Coding: 15235
Shop #: WSC 00000
VCID: 275D9C51C5AFC6061F-5124
WVWAE63B25E054822 VWZ7Z0D0380077

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway Labels: 6N0-909-901-19.lbl
Part No: 6N0 909 901
Component: Gateway K<->CAN 0001
Coding: 00006
Shop #: WSC 05311
VCID: 70EFB70D30E1C1BE8E-5124

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv. Labels: 1C0-959-799.lbl
Part No: 1C0 959 799 C
Component: 08 Komfortgerát HLO 0004
Coding: 00258
Shop #: WSC 05311
VCID: 377D4C11150F56868F-4B1A

Subsystem 1 - Part No: 1C1959801
Component: 08 Tõrsteuer.FS KLO 0202

Subsystem 2 - Part No: 1C1959802
Component: 08 Tõrsteuer.BF KLO 0202

Subsystem 3 - Part No: 1C0959811
Component: 08 Tõrsteuer.HL KLO 0202

Subsystem 4 - Part No: 1C0959812
Component: 08 Tõrsteuer.HR KLO 0202

2 Faults Found:
00929 - Locking Module for Central Locking; Front Passenger Side (F221)
27-10 - Implausible Signal - Intermittent
00930 - Locking Module for Central Locking; Rear Left (F222)
27-00 - Implausible Signal

-------------------------------------------------------------------------------
Address 56: Radio Labels: 3B7-035-1xx-56.lbl
Part No: 3B7 035 180 G
Component: Radio PM6 0016
Coding: 04031
Shop #: WSC 05311
VCID: 24478B5DB4992D1E3A-5124

No fault code found.

End-------------------------(Elapsed Time: 04:53)--------------------------

 

[scoobysmak]

Humm... the only thing that sticks out to me is this.

"1 Fault Found:
16683 - Boost Pressure Regulation
P0299 - 000 - Control Range Not Reached - Intermittent
Freeze Frame:
RPM: 2142 /min
Torque: 210.0 Nm
Speed: 57.0 km/h
Load: 45.9 %
Voltage: 13.98 V
Bin. Bits: 00101000
Absolute Pres.: 2091.0 mbar
Absolute Pres.: 1652.4 mbar"

Just ran a search for the P0299 code and got this link:
https://forums.tdiclub.com/showthread.php?t=271408

 

[1854sailor]

VAG Code 16683 is what is putting the car into limp mode.

Double check ALL of the boost hoses and their connections. The hose that goes from the turbo to the crossover pipe is a good place to start. There is a wiring harness that rubs a hole in that hose if not moved and secured with a wire tie. There are four seals that can leak and cause this; a telltale is an oily deposit around the joints. As others have suggested, the N75 Valve is another cause. Was the VNT Actuator calibrated when the new turbo was installed? One last thing; a dirty EGR Valve has been known to cause this by not fully seating. Pull it and see how it looks.

From the Ross-Teck Wiki Pages: http://wiki.ross-tech.com/wiki/index.php/16683/P0299/000665

Good luck and please report back.

 

[Tom_B]

x2 on checking all the boost hoses and connections. Flaws and splits cannot necessarily be seen just looking at the hoses in place. Take them off, wipe them clean and pore over them closely. Flex them back and forth. There are many threads regarding these issues, your symptom is not uncommon, and the solution is not always easy to find.

One last comment - do you have a tune? After I got RC1 mine started to have the same issue, sporadically. Often under load while gradually pulling a long shallow hill, but under different conditions also. Several of us with RC1 have occasionally experienced the same underboost code. Speculation is there could be something minor in the mapping. I've been through the entire charge air path, replaced most, if not all, the hoses and O-rings, N75 and vacuum hoses and it still occasionally does it. On balance I'd still rather have the tune though.

Do report back if you find the solution.