P0234 - Overboost - 1.9l TDI

nvdtdi

Member
Joined
Jan 15, 2011
Location
Burford
TDI
2002 Jetta TDI
Im new to the tdi world, and my cel came on last week and i found out it was code p0234 - overboost.. i have done some research and what not. and a lot of the things i have read said its either MAF, turbo actuator, vaccum leak or N75 valve....

I have replaced the MAF and didnt solve the problem. my next step was to see if the Turbo Actuator is goor or not. I have read up on it and what not but my question is:

Turbo Actuator
Where is it located in engine bay?
Whats easyest way to access it, looking down or jacking car up and looking up?
How can I tell if its good or not with out taking the hole mani off?

N75
Where is it located in engine bay?
Whats easyest way to access it, looking down or jacking car up and looking up?
How can i tell if its good or not?

I have tried to search for answers but had no luck..

Any other help would be much awesome! Thanks
 
Last edited:

jcrews

Top Post Dawg
Joined
Jul 28, 2007
Location
Round Rock, TX - VCDS
TDI
All gone
See below.
Im new to the tdi world, and my cel came on last week and i found out it was code p0234 - overboost.. i have done some research and what not. and a lot of the things i have read said its either MAF, turbo actuator, vaccum leak or N75 valve....
I have replaced the MAF and didnt solve the problem. my next step was to see if the Turbo Actuator is goor or not. I have read up on it and what not but my question is:
Turbo Actuator
Where is it located in engine bay?

On the turbocharger (exhaust manifold), between the turbine and compressor housings.

Whats easyest way to access it, looking down or jacking car up and looking up?

It's easy to reach from above, but not bad from below either. I find it easier to work on from above.

How can I tell if its good or not with out taking the hole mani off?

Use a hand vacuum pump. Attach your pump to the actuator line, and pull a vacuum. If it leaks, check the hose; if the hose is OK, replace the actuator. If the actuator holds vacuum, but does not move, or is stuck all the way down, remove the small clip (be careful not to lose it) from the vane control arm. Loosen the two nuts that secure the actuator with a 10mm wrench, so you can disengage the control arm from the actuator rod. If the arm moves freely, but the actuator is jammed, replace the actuator.

N75
Where is it located in engine bay?

On the firewall, left side (driver side), near the brake booster. It has a gray top.
Whats easyest way to access it, looking down or jacking car up and looking up?
How can i tell if its good or not?
This item doesn't fail often. An electrical failure will be detected by the ECM, and a physical failure may appear as poor/inaccurate charge pressure control if all else is in good working order.

I have tried to search for answers but had no luck..
Any other help would be much awesome! Thanks
 

nvdtdi

Member
Joined
Jan 15, 2011
Location
Burford
TDI
2002 Jetta TDI
awesome, thanks a lot jcrews.. i will see what i can do, not sure about today as its -27 outside.

Thanks
 

DieselDrink

Veteran Member
Joined
Jan 20, 2006
Location
Etobicoke, ON, Canada
TDI
2001 Golf TDI 1.9L
Funny. Not getting a code thrown yet buy also in-20 weather have noticed some overboost. I aspect my actuator is fine, but maybe really cold makes things stick?

Or vacuum lines are 10 years old. Could be that?

What about N75? Also over 10 years old.
 

mrrhtuner

Veteran Member
Joined
Mar 29, 2011
Location
London Ont Canada
TDI
2003 Jetta Wagon TDI, 2015 Passat TDI, 2015 Touareg TDI
Funny. Not getting a code thrown yet buy also in-20 weather have noticed some overboost. I aspect my actuator is fine, but maybe really cold makes things stick?

Or vacuum lines are 10 years old. Could be that?

What about N75? Also over 10 years old.

Sorry to bump this really old thread, but I figure it's sometimes better to build on one thread then have multiple small threads.

I am experiencing a similar issue.

When I purchased my 03 wagon last winter, I would get limp mode and overboost P0234 error code often. Once spring/summer/fall were here, I hardly got the code nor experienced limp mode.

Most recently, when it was about -18 Celcius outside and I was driving on the highway about 60 minutes round trip, my car would continuously go into limp mode.

Torque Pro pulled these codes:

-P0234 - Turbo overboost condition
-P3400 - Cylinder deactivation system bank 1.

Now the P0234 is common, I've been spending the past hour reading up on it at work but the P3400 doesn't seem to be that common or common at all on our TDI's.


This is all happening on my 2003 ALH wagon.
 

Rembrant

Veteran Member
Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
When I purchased my 03 wagon last winter, I would get limp mode and overboost P0234 error code often. Once spring/summer/fall were here, I hardly got the code nor experienced limp mode.
Most recently, when it was about -18 Celcius outside and I was driving on the highway about 60 minutes round trip, my car would continuously go into limp mode.
Have you done anything to the turbo or vacuum system since you bought the car? Maybe somebody changed the VNT actuator previously and didn't set it up properly?

If it was me, I'd give the VNT actuator and vacuum system a check-up. If the vacuum lines have not been changed, then I'd change them...all of them. I'd clean out the N75 while I was in there...contact cleaner or similar spray in the ports and blow it out. Check the nipple on the vacuum pump for looseness and repair if necessary.

I'd also check the VNT actuator movement and set-up. Make sure the stroke starts and stops at the correct amount of vacuum. Make sure the VNT actuator rod isn't sticking due to rust on the lower part of the rod.

Make sure the VNT lever on the turbo moves nice and free. With the VNT actuator disconnected, the lever should feel loose and easy to move for the full stroke, back and forth.

That's what I'd be checking. I'd say that either the VNT actuator isn't adjusted properly, or something is sticking...the VNT actuator rod, the VNT mechanism itself, or maybe N75.
 

mrrhtuner

Veteran Member
Joined
Mar 29, 2011
Location
London Ont Canada
TDI
2003 Jetta Wagon TDI, 2015 Passat TDI, 2015 Touareg TDI
Hey Rembrant,

My mk4 wagon was serviced by a club member a few years ago. Actuator looks to be in fine condition.

I have replaced all the vacuum lines. My EGR last I checked in early spring looked fine and the intake manifold looked to be in acceptable condition inside.

I'm not doubting you as I am newish with turbo troubleshooting, but from what I've read, even if the VNT actuator is not setup perfectly, woudn't I get issues year round and not just in winter?

Since having my car go into limp mode crazy last week with the CEL, it's been great since with minimal limp mode and no CEL...but then again, the really cold temps haven't came by.

I found a few guides on testing the actuator, I will give that a shot and follow what I found on trying to identify if the vanes are sticky or not.
 

Rembrant

Veteran Member
Joined
Oct 31, 2014
Location
Canada's Ocean Playground
TDI
2013 Golf TDI DSG
I'm not doubting you as I am newish with turbo troubleshooting, but from what I've read, even if the VNT actuator is not setup perfectly, woudn't I get issues year round and not just in winter?
Well, sometimes problems just decide to be random. If you've done some reading, then you may very well know more about the topic than I do. I haven't had to deal with any overboost issues on any of my TDI's yet. I was just throwing ideas out on what I'd be looking at if I was in your shoes.

Without knowing what the problem is, sometimes you're really left with going through the system inch by inch.

If your vacuum lines are confirmed to be all good, and your vacuum system is working properly @ (25"/hg+), then that really leaves only three things...N75, MAP sensor, and turbo/VNT actuator. So, knowing that N75 failures are rare, and MAP sensor failures are even rarer, it comes back to the where the problems usually show up...at the turbo, either due to a sticky/problematic VNT actuator, and sticky/dirty VNT vanes in the turbo itself. Just theorizing.:D

At the end of the day, it could be what Dimitri16v mentioned above...I dunno. A friend of mine was having overboost issues/codes in the middle of last winter with his 05 BEW wagon. Once the weather warmed up, the problem went away and hasn't returned since. That was a year ago.
 

jbruAT09

Member
Joined
Nov 23, 2014
Location
maine
TDI
2002 Jetta
A year late to the party. ive had an 02 ALH for a few years now. Every year going into winter or into the spring my turbo seems to go into lag for a few days to a few weeks. While its painful driving at highway speeds with no turbo, after a few days it generally goes back to spooling and running normal. Having said that, for the first time today, the CEL came on with the P0234 code. In the past no codes are thrown, but it doesnt take an expert to know the turbo is not spooling. On the flip side, there have also been times when the turbo is clearly overboosting-loads of power, and still no codes. I have also had a hose come of the N75 on its own.
A friend of mine lost his turbo at 380K, but i think at 260K im ready for a new one.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
I'd thoroughly check your vacuum pump's nipple. Issues of temperature affecting things tends to point toward excessive thermal fluctuations. Even have read where a vacuum line to the turbo actuator would collapse when things got warm/hot.

I also believe that there have been reports of icing either in the vacuum line or at the nipple to the actuator. I recently experienced fuel blockages on my tractor to what I can only claim to have been a very small formation of ice at the nipple heading out the tank.

Pay particular note to what air temperatures and humidity levels are doing as this may show a pattern.
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
I recommend pulling the vacuum actuator arm off the actuator lever and moving it by hand.
A bit tricky to do on the car, but, doable.
I learned the first time I ever took the clip off to hook some good strong thread to it before attempting to put it back on.
If you drop you still know where it is, on the end of the string

I had to do this the other day and the VNT opened great, however, wouldn't close worth a damn.
I imagine what You can see in the pictures in the link below, maybe not so bad but still pretty bad.
http://forums.tdiclub.com/showthread.php?t=417055
 
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