16618 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)

[Passat 2.0tdi]

Hello all,
My Passat 05 2.0tdi 105 B6 model has been going in to limp mode a few times when driving on the motorway usally at going uphill- pulling over on the hard shoulder and restarting the car has sorted it out when VCDS scanned- it came up with 16618 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition), I've read a few posts with people suggesting N75 valve,sticking vanes-but does anyone know B6 specific information ?

Thanks in Advance

[a8 tech]

I have never never found a single problem with a n75 valve after 20 years working for vag, often replaced because people don't understand how they operate.
Check the turbo via final control output test for full movement of the actuator also check with a mitivac for any leaks on the vacuum pipes and the actuator.

[DSG4ME]

I have never never found a single problem with a n75 valve after 20 years working for vag, often replaced because people don't understand how they operate.
Check the turbo via final control output test for full movement of the actuator also check with a mitivac for any leaks on the vacuum pipes and the actuator.

My mates Touran has been doing this lately, it's done around 90k now, and his mechanic is suggesting it's the ECU doing it, he also gets the glow plug light and the ESP light come on when it happens, have you come across this before?

Also as you work for the group, have you come across a cold start hesitation, and is there a cure for it yet, seems to be a lot of USA user's suffering from it both in manual and DSG forms, and do you think a possible cause could be a dirty fuel filter, it seems to happen until the temp gauge hit's just above the 70 degs mark, then clears itself, also one other trait of it seems to be if you turn off and start again soon after starting originally, there are many suspects in my eyes ranging from fuel and temp and possibly lambda sensors, to the current fuels sold to us, as bio creeps into the mix, so does the chance of it not being suitable in PD engines.

tia.

[Teflon]

a8Tech (as usual) is bang on the money. I had 6 months of all sorts of diagnosis on my A6 for this problem before finally nailing it as a sticky turbo. We had MAP sensor, crankcase pressure sensor, fuel filter MAF sensor, N75 and some others suggested, before I found the solution here on the forum.

You don't give any info about the car, but if you are 40-80k miles, gently driven, then you are in prime territory for the turbo to be gunged up with carbon and restricting the VNT mechanism. If it is that, you will find some people recommending to fix it it by pouring some wonder juice in your engine, but at best it is only a very temporary fix and the only long term solution is to crack the turbo open and spend an hour cleaning it out.

Here's hoping you have a vacuum pipe leak instead!

[martin1810]

A MAP sensor can read "overboost" when it shouldn't so this could be at fault. The N75 valve can jam and not bleed vacuum to the air filter but this is very rare. The turbo vanes can be sticking which is very common. Vacuum leaks don't usually cause "overboost" on a passat. The cheapest option is to replace the MAP sensor (which I doubt is faulty). The most logical thing would be to remove and clean the turbo.

[Passat 2.0tdi]

I have never never found a single problem with a n75 valve after 20 years working for vag, often replaced because people don't understand how they operate.
Check the turbo via final control output test for full movement of the actuator also check with a mitivac for any leaks on the vacuum pipes and the actuator.

Can anyone help me to use VAG com for checking the actuator as suggested by a8 and or tell me the position of it and what it looks like on a passat 2.0 tdi 2005 b6 model. Thanks again

[Teflon]

Can anyone help me to use VAG com for checking the actuator as suggested by a8 and or tell me the position of it and what it looks like on a passat 2.0 tdi 2005 b6 model. Thanks again

Can't help with that, but I can offer a quick a dirty option to give you a clue. There are full instructions, complete with a helpful video on tdiclub.com somewhere in the "TDI 101" thread. Try this http://forums.tdiclub.com/showthread.php?t=140910.

Your turbo will be different from the one shown (as was mine), but the same principle applies to most of the VAG TDi turbos.

Basically, locate the turbo and spot the vacuum actuator. The output rod from this is connected to a little lever. You can release the clip making this connection, push the actuator out of the way and operate the VNT lever manually. It should move freely, with a satisfying clonk at both ends of its range. If it feels stiff or gritty, or if it doesn't seem to have a full range you have a gunged up turbo.

One word of warning - do not try to remove the actuator or mess with the adjustment on the actuator rod. It is all factory set up to get the correct boost at a given level of vacuum applied to the actuator and I'm told that if you muck about with this you risk a whole heap of problems.

If you feel like getting your hands dirty to fix the problem, I've got a set of instructions with photos. Saved me about £700 on the price of a recon unit.

[billcoleman]

Hi Teflon. I would greatly appreciate some instructions on how to clean-out my turbo. What started as the occasional overboost/limp mode is occuring almost every day now.

I know it is overboost because I have a VAG com set.

I can do almost anything on a car, but have never stripped/cleaned a car turbo before (I have overhauled a ships turbo though - about 30 years ago), so a few starters would be great.

Bill

[Teflon]

Hi Teflon. I would greatly appreciate some instructions on how to clean-out my turbo. What started as the occasional overboost/limp mode is occuring almost every day now.

I know it is overboost because I have a VAG com set.

I can do almost anything on a car, but have never stripped/cleaned a car turbo before (I have overhauled a ships turbo though - about 30 years ago), so a few starters would be great.

Bill

Hi, Bill.

Most of what you need is in the link I provided. Once you have confirmed that it is indeed the turbo that has to be cleaned out, the most important part is to be well organised and methodical. I took plenty of photos and made notes on the way.

When removing the turbo, ensure that everything is labelled and that you take care with the oil feed and return pipes. Don't allow any contamination. Some people recommend that the feed pipe is replaced and if there is any gunk at all inside I would suggest you get a new one. On some models, it is easier to take off the exhaust manifold complete with turbo but on my A6 2.5TDI we could get at the turbo from above and underneath. Taking it off was the hardest part.

Once off, mark the turbo housing to provide some alignment points for re-assembly. Disconnect the actuator but do not interfere with its adjustment. Split the casing by removing the six bolts (it may need lots of easing oil and some gentle persuasion with a brass chisel) and be very careful not to damge or ding either of the impellers.

You will find the hot side of the turbo is very stiff with hard carbon deposits. Prior to disassembly, take plenty of photos and note the position of all components, including the acutator ring and how the vane levers are positioned. If you don't do this then putting it back together will drive you nuts. The ring is held by 3 rollers on pins, don't lose them. Mark the position of the actruator ring before it comes out 'cos it only goes back in one specific arrangement. The mechanism itself is held by 3 allen set screws - be very careful not to snap these if they are stiff, use plenty of oil and lots of patience.

Once taken apart, you can get stuck in with a brass chisel, emery paper, parrafin and scotchbrite. The vanes can be cleaned if they need it but don't try to remove anything from the impellers in case you unbalance them. The bearings should be smooth and not feel rough. If there are any problems then I'd recommend a refurb.

Once you can see shiny metal, put everything back together. The mechanism should work with a satisfying metallic clonk. Don't worry if there seems to be quite a bit of slack - the tolerances are quite wide so that it doesn't sieze up when stinking hot. Pre-charge a bit of oil into the turbo oil feed so that it isn't starved on start-up.

Just in case anything went wrong I had priced up a refurbished turbo on 24 hour turnaround. I broke one of the set screws but got away with it. Once back on you don't need to do anything with VAGcom, just start the engine and everythign works okay.

If you PM me an E-Mail address I'll send you some before, during and after pics.

[hissinsid]

Thanks guys, lots of great info there. My 07 B6 2.0tdi Passat is showing exact same symptoms. i.e. goes into limp mode on overtaking occasionally (but becoming more frequent). VCDS scan gives the following:
1 Fault Found:
000564 - Boost Pressure Regulation
P0234 - 006 - Limit Exceeded (Overboost Condition) - Intermittent
Freeze Frame:
Fault Status: 00000001
Fault Priority: 5
Fault Frequency: 1
Reset counter: 35
Mileage: 215789 km
Time Indication: 0
Date: 2000.00.00
Time: 05:42:49


Freeze Frame:
RPM: 2592 /min
Torque: 360.0 Nm
Speed: 90.0 km/h
97.50 %
Voltage: 14.35 V
Pressure: 2321.7 mbar
Pressure: 3003.3 mbar
Am thinking of cleaning the turbo, checking the flap valve etc so ANY procedures/photos very much appreciated.

Steve