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2004 BEW Limp Mode Boost Issue

26009 Views 12 Replies 6 Participants Last post by  Davidloc
Hi There,

I have a 2004 Jetta Wagon TDI with the BEW motor. The car has been going into limp mode nearly every day especially on very cold mornings while going up hill. I unfortunately I did not copy down the code that was thrown but it was related to an overboost condition.

***Start Edit
16618 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
P0234 - 000 - -

I took car out for a test drive an was able to make it go into limp mode again and reproduce the fault code above. I also checked the MAF via VCDS and it seems to be fine as the actual tracks the requested up to ~800 or so and back again.

***End Edit.

Today I replaced all vacuum lines (one at a time), the N75 valve, and the check valve. By inspection the old check valve was broken (i.e. air flow in both directions = bad). I saw some minor wear on the vacuum lines but nothing special to note. I can freely move the actuator with my finger and have run the output test to verify that N75 is indeed moving the actuator under vacuum.

However, I am not convinced that the car is fixed. Please see that attached image of the VCDS scope screen. This plot is the result of revving the engine while in the driveway. The specified boost and the actual boost do not track as I think they should (per the 1000q faq). As you can see the actual is significantly higher than the requested.

Any ideas where to check next (MAP sensor maybe)? I would really appreciate any help that could be provided. I have searched the forums and faqs for weeks which led me to replace the vacumm system parts. Now it is time to ask for help directly.



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Hi There,

Thanks for your reply. I should have been more clear in regards to the actuator. It can be moved about 3/4" against the spring freely (i.e. without any snags along that length of travel). The actuator then returns to it's default position upon release. This is when it is connected to the lever.

When I was replacing the vacuum lines I took a look at the wiring to the VNT but did not see anythig that stood out right away (i.e. broken wires). Where do failures typically show up in the harness? I did not inspect the MAP due to it being tucked under the headlight.

I did notice a bit of blow by around the MAP area near the windhiled wiper resevoir. Maybe a boost leak test should be the next step?

Thanks again!
So today has been a busy day on the car.... with very little achieved...

1. Took the front end apart to get to the MAP sensor only to find out that the one that was shipped is incorrect for this car (too large).

2. Discovered that oil slick under the washer fluid tank was due to a broken intercooler hose retaining clip. I took this all apart. Cleaned the area and all the parts. I replaced the seals and reassembled with a new reatining clip.

3. Took apart all other pipes from turbo to intercooler and cleaned/replaced all seals. I then reassembled.

4. I attempted a boost leak test.

- installed boost leak cap (from turboboostleaktester.com) at the at the MAF junction.
- removed oil filler cover.
- used a wine bottle stopper to plug the PCV hose.
- set compressor at 5psi.

I connected compressor to boost leak cap. No pressure build up!! I disconnected the intake pipe at the EGR and put my hand over the end of the hose. Pressure immediately built up to 5psi. If I had my wife hold the compressor fitting to the cap and I used a plastic bottle pressed firmly against the intercooler to EGR pipe we could build pressure to 10psi. Under pressure there did not appear to me any major leaks in the piping.

However, my understanding from the FAQ was that I should be able to build up pressure with the intercooler EGR hose connected. What am I missing here? Help!!!!!

5. I hooked of VCDS and monitored block 11. The results are the same. Actual does not overlay on specified as shown in previously posted pic.

Any additional info would be greatly appreciated.

Thanks ahead of time.

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Some more detail which sort of turns my stomach.

Still not being satisfied with the efforts of the day, I put my vacuum gauge on the actuator again.

Movement of actuator starts well below 5inHg. Max stoke of actuator is at 7.5inHg. Applying more pressure (up to 20inHg) does not geneate any additional movement.

This would seem answer the overboost condition. Car requests a particular boost (say 5inHg) for a particular RPM expecting a low amount of boost. However, actuator at 5inHg is nearly at max stroke generating more boost than is required. The car then in turn demands less boost (the low power case).

Additionally the vacuum slowly leaks off of 7.5inHg rather than holding steady. If I put my finger over the end of the vacuum tester line the gauge holds steady ruling out a leaking gauge connection. The actuator should hold vacuum correct?

Can the actuator be adjusted? If so, what is the proper method?

Can the actuator ONLY be replaced on the BEW? I think I read somewhere that the answer was NO but it is unclear how old that post was.

Again, any help would be greatly appreciated.

Thanks ahead of time.
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BEW Turbo Replacement Actuator Found and Installed!!

Hi There,

It has taken a couple weeks to work on the car due to other commitments but the result is a success story that I hope will offer some relief to all of the folks out there that have a VW with a BEW TDI motor. If someone else has already come up with this solution, please add this as another data point. I spent weeks searching forums for solutions and came up with only one answer: replace the turbo.


I was able to successfully replace the stock turbo vacuum actuator for the Borg Warner KP39 turbocharger (standard equipment on the BEW motor) with a Garret Smart Actuator (typically found on Garret VNT17 replacement turbochargers). The Garret Smart Actuator has the same stroke and sensor output as the Borg Warner unit since the VNT17 is meant to be a bolt on replacement for the KP39.

The Details:

1. Garret Smart Actuators can be found at the usual places (i.e. idparts, kermatdi etc.) for ~$120.
2. The Garret unit mounts with (2) M6x1 studs to a mounting plate.
3. The Garret unit uses a ball and socket mechanism to attach to the vane lever on the VNT17. This can be removed and an extension rod can be fabricated to attach to the Borg Warner vane lever.

The Solution:

1. The key to making this swap is getting the (2) bolts that hold the actuator bracket onto the turbo housing out. If you break them you will either need to come up with a clever mounting bracket to mount the actuator to the exhaust down pipe studs or remove and disassemble the turbo. There is not enough clearance (i.e. a straight drill path) to drill and tap the holes. Use lots of penetrating oil and be patient. It does not take a lot of force to snap an M6 bolt. I know this from experience.
2. Once the (2) bolts are removed, remove the 10mm nut on the top of the actuator rod.
3. Remove the actuator/actuator bracket assembly from the car.
4. The actuator is tack welded in (4) holes located on tom of the actuator. Drill these out. Gently use a small chisel to separate the bracket from the actuator body. To drill out the welds I had to bend the actuator rod out of the way.
5. The bracket is made of (2) pieces (the actual bracket that holds the actuator and heat shield) that are riveted together. To make machining easier drill out the rivets to separate the bracket pieces.
6. Drill (2) 0.25" holes in the actuator bracket with a center to center spacing of 1.3". These holes will most likely run into the existing holes. The center line between these holes should be parallel with the flange on the bracket such that when the actuator is attached the connector and vacuum port points towards to passenger side of the car.
7. Drill and tap the rivet holes for a 10-32 screw.
8. Mount the Garret actuator the actuator bracket using (2) M6x1 flanged nuts.
9. Reattach the heat shield to the actuator bracket using a couple 10-32 screws and lock washers.
10. Install rod extension onto Garret actuator rod.
11. Install M6x1 nut on actuator rod (lower stop nut).
12. Reinstall actuator assembly in car.
13. Draw a vacuum of 20in on the actuator.
14. Adjust the nuts on the actuator rod such that the vane lever is at the mechanical stop at 20in vacuum.
15. Install M6x1 nut on top of actuator lever (upper stop nut).
16. Verify that movement of lever starts at 3-5in and stops at 20in. This took me a couple times to get right.
17. Reattach vacuum line from N75 and position sensor connector.
17. Hook up VCDS and go for a test drive.
18. From Bentley you need the car to be at operating temperature and under load. A good long hill lugging in 4th gear at 1500 RPM make for a good plot.
19 Go to measuring block 11 and use the VC Scope to plot the RPM, specified Boost and Actual boost. These should closely match as detailed in the 1000q testing section. Testing with no load will not produce obvious results. You must be under load. Overshoots and undershoots are expected but in general they should track with each other.


If I may rant for a moment... Although I can sort of understand why making someone replace an entire good turbo ($1000) just because the actuator ($120) is bad (and are known far and wide to go bad) is a lucrative business for the turbo manufacturer, it is a poor design decision which may result is many customers moving to a different brand. I am very disappointed that VW let this one slip by.

What would this cost the average person: $1000+ for parts and $1000+ for labor? $2000+ Really?? Simply unacceptable. I solved the problem for $120 and a day in the shop.

Please see that attached picture of the retrofitted assembly. If enough people are interested I was thinking of making a bunch of actuator extension rods, putting together a hardware kit and maybe some more detailed instructions. I probably could put it all together for maybe $20-$25 a kit.

Let me know if you would be interested.

Thanks for all your help.


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