VNT turbo actuator adjustment and repair/replacement on TDI engine-mk4

Aug 14, 2014
VNT turbo actuator adjustment and repair/replacement on TDI engine-mk4
  • How to diagnose, test, or replace the VNT turbo actuator on a TDI engine and then adjust the rod

    This article shows how to test or replace the turbo actuator on a TDI engine (vacuum actuator)

    difficulty: 2/5

    All mk4-mk6 VW and Audi TDI (except the Touareg, Q7, and Porsche Cayenne diesel) use a vacuum actuated rod to move the vanes inside the VNT turbo. A sticky VNT turbo actuator can cause limp mode by not moving the vanes as the car computer expects. Dealers usually replace the entire turbo because they make more money and it increases the chance of fixing the symptoms in 1 visit. Failed or sticking vanes inside the turbo or the vane control ring inside the turbo can cause the same symptoms. This article shows how to isolate the problem and replace the actuator.

    The VNT actuator looks like a wastegate can and uses a lever to move the VNT vanes inside the turbo. VNT actuator and wastegates are similar in location and appearance so don't get confused if you see the term wastegate used instead of VNT actuator. The biggest difference between them is that a wastegate can uses pressure to work and is only found on older mk3 TDI. The VNT actuator on mk4 Garrett turbos uses vacuum to suck its rod in. Borg Warner actuators found on newer TDI use vacuum to push their rods out.

    It's possible to adjust the VNT rod to adjust its movement but before you try this, carefully check and replace all vacuum lines and other possible maintenance items. If it was working fine before, do not adjust the VNT rod. Only adjust the VNT rod if it was out of adjustment before or you are modifying the turbo or turbo setup. Adjusting it when it doesn't need adjusting will not improve turbo response or fuel economy and could cause dangerous boost spikes or lack of response.

    Other non pumpe duse mk4 TDI engines are similar. 2004-2006 mk4 pumpe duse 1.9L TDI, 2005-2006 mk5 Jetta, and 2009+ common rail 2.0L TDI use an actuator with a sensor to see rod position. A common problem with these is broken wiring at the actuator. Carefully inspect the wiring if you have a 2004+ Jetta/Golf/NB.

    Related links: 1000q: fixing limp mode and 1000q: constant low power or can't rev. Also see 1000q: ALH/BEW turbo removal and 1000q: turbo vane cleaning.

    FOR THE BEW ENGINE, see 1000q: BEW actuator replacement.

    2004-2005 mk4 Passat TDI use the non-sensor can.

    For the mk5 or newer engine, see 1000q: mk5+ TDI actuator replacement and testing. I suggest reading both articles to gain a greater understanding of the system and I may have left something out of one article.

    Garrett (GT) and Borg-Warner (KKK) turbo actuators work in different directions. Garrett actuators suck in the rod with vac vs. push out the rod with vac. My mk5 BRM engine Borg Warner actuator pushes out starting around 3" vac and is fully extended around 17-18".

    VW Touareg, Porsche Cayenne diesel, and Audi Q7 use an electric actuator for the turbo so the testing and diagnosis is completely different. mk7+ cars also use an electric actuator.

    If you find the tips on this page helpful, please use the donation button at the top so that I can continue to keep publishing great articles. The Bentley service manual is about $80 and doesn't even mention this repair - it just tells you to replace the entire turbo! This page has videos, color pictures, and greater detail. I know it's saved many people from a much more expensive repair. Thank you in advance!

    How the VNT turbo actuator should work
    The lever on the outside is welded to a lever inside the turbo housing. This is how it moves the VNT vanes. See the below videos to see how smoothly and free the lever should move. It should not stick or bind at all. Vacuum is being applied to the can, not pressure. When there's no vacuum (engine off), the rod is fully extended because the spring inside the can is pushing it open. As engine rpm goes up and more turbo boost is requested by the car's computer, the N75 solenoid allows vacuum pressure to go to the can and the rod retracts under vacuum pressure. In other words, at full vacuum, the lever should be at the stop screw (not visible). This moves the internal vanes and gives more boost. At full rest, the rod should be fully extended but not hitting anything. Because this relies on vacuum pressure, it's essential that the vacuum lines and N75 solenoid/wiring are working and not leaking.


    The lever moves a ring and the ring moves the vanes. These vanes change the angle and speed of exhaust hitting the turbine wheel.


    Here's a newer video I made.


    Again, dealers prefer to replace the entire TDI turbo and actuator as a unit because it costs more and because it also rules out any internal turbo/VNT vane sticking problem. Below is an example of a sticking actuator. It holds vacuum but doesn't have full or smooth movement.


    Here is a video showing good actuator movement.


    Once the engine is fully warmed up, you should rev the engine high and hard on a regular basis, like when entering highway on ramps (always observe posted speed limits), to raise exhaust gas temperatures (EGT). Raising EGT will burn up and blow out carbon and soot build up out of the VNT vanes and help prevent them from getting stuck. Only do this once the engine is fully warmed up and let the car cool down with a period of normal driving afterwards. The key is both high rpm and high load. High load at low rpm or high rpm in neutral with no load will not raise EGT high enough and long enough to burn up the soot.

    Before you order a replacement VNT actuator, spray some penetrating lubricant around the VNT lever as described below and go for a few hard runs. You might go into limp mode a few times but it's free and it may solve the issue if the problem is only minor soot buildup. The problem isn't from only vane movement because if you monitor VNT movement through VCDS, it reaches full movement at a relatively low RPM. The key is both high rpm and high load (temperatures) to burn up and blow out the buildup. Another problem is corrosion buildup around the adjuster ring inside the turbo.

    Limp mode with underboost is safer than limp mode with overboost. Have the car scanned for codes and use a boost gauge to confirm which you are getting.

    Also see the TSB for VNT actuator replacement with pictures and procedures in the exclusive content forum
    [​IMG]
    Parts (click links to compare prices)

    Note - The ALH engine (1998-2003 TDI) is a little different from the BEW engine's (2004-2006 4th gen TDI) VNT actuator because the BEW's actuator has the "G500 sensor" to determine vane position. This is also called the smart actuator. See additional notes below.

    VNT actuator for ALH engine (up to 2003): VW# 038 198 716, available from kermatdi VNT actuator

    1 circlip/e-clips for the actuator lever and 1 spare - no VW# is available but a 1/4" e-clip should work. The spare is for when the first one flies off and disappears. If you know the correct size/shape, please post your comment in the myturbodiesel forums, thank you!

    I avoid any actuator sold by [​IMG]since it's almost certainly a cheap copycat part. I also had a bad experience with this seller so never again. Cheap actuators may not have the spring set to the proper resistance, in which case you'll never be able to adjust the actuator correctly.

    The Garrett part comes with a clip taped to the box as shown right.

    If you have the BEW or similar engine (2004+) you need the smart sensor actuator. There is no official VW part number for it because VW does not sell these separately from the turbo. Borg Warner doesn't sell them either. They can be purchased from kermatdi smart VNT TDI actuator and custom modified to fit.

    There is no BRM actuator available but you can make a custom bracket to attach the CBEA/CJAA actuator. It will work fine. The Borg Warner (KKK) actuator rods suck out instead of sucking in because the spring is on the other side of the rubber diaphragm.

    CBEA engine turbos have an actuator available, VW# 03L 198 716 a. This will also fit CJAA engines.

    Procedure

    First confirm bad VNT or isolate another problem
    First confirm the diagnosis of a sticking VNT actuator because it could also be a sticking turbo VNT vane, bad n75 solenoid, or leaking vacuum line.

    Have a helper turn on the car and the VNT lever should move. If you have a VCDS cable from ross tech, with the engine running, click on "engine" and then "output tests". One of the tests is N75 test cycle. This cycles the n75 solenoid, VNT, and vacuum line.

    A common problem is soot and carbon clogging the VNT vanes which causes the same symptom as a sticking VNT lever. See the VNT turbo cleaning DIY in the FAQ to see a detailed cleaning procedure.

    Through VCDS, log requested boost vs. actual boost. To do this, plug in your VCDS cable to the obd2 port under dashboard, near the steering wheel. Click on "engine". Then click on "measuring blocks" in the below screen.
    [​IMG]

    Then click "up" or enter 11 to view "group 11" and graph to see the below screen. If it's not close then this could indicate a defective or clogged VNT actuator, N75 solenoid, vac lines, or sticking vanes. Here is an example of a good N75 solenoid-vac lines-VNT actuator-clean turbo. Suddenly stomping on the accelerator pedal will produce spikes - this is normal. Smooth, normal acceleration should produce minimal spikes. A healthy ALH engine should see a spike and then see the boost settle down to about 1900 mbar. Swap the N75 solenoid with the EGR solenoid as a test to isolate a possible solenoid problem and check the vacuum lines. This will isolate a boost problem to the VNT actuator or internal vanes. To further isolate those, do the tests below.
    [​IMG]

    First put a few drops of PB Blaster on the VNT lever and then go for a test drive. This may loosen surface rust enough to get correct movement. You may have to remove the rubber elbow before the intake manifold and turbo intake plastic hard pipe for clearance. Below is a picture of the passenger side with those hoses removed. While this won't free a seized VNT vane, it won't hurt anything either. Warm up the engine and then go for some very hard runs as described above.
    [​IMG]

    Here is the turbo out of the car for illustration (as if you were looking at the back of the engine). Put a few drops of PB Blaster around the lever and circlip to help them move smoothly. (There's a heatshield around the can, not pictured). If you try to press the lever down by hand, you should feel smooth, consistent resistance from the spring inside the VNT actuator. After you release the lever, the spring should immediately push it back up to the top resting position. Full travel from the stop is about 1cm and can be seen in the above videos.
    [​IMG]

    Follow the vac line to the N75 solenoid valve (solenoid is mounted on middle of firewall - look above the brake fluid reservoir). Remove the vacuum line at the N75 solenoid valve and apply vacuum to the line. The rod should move smoothly beginning at about 3-5" vac and hitting the stop at 18-22". Full travel from the stop is about 1cm. You can also use your hand (on a cold non running engine only!) to feel the rod move as you apply vacuum to it. It should move smoothly with no binding or clicking.

    For reference, here are the BRM engine's (2005.5-2006 Jetta TDI) actuator specs: during the test, do not exceed 750 mbar. The linkage should start moving at around 300 mbar and be at the end at about 700 mbar. The actuator lift should be 10mm.

    If the VNT actuator is not holding vacuum then the VNT actuator is bad (since you've already checked and rechecked the vacuum lines). Replace it.

    If it's binding, clicking, or not moving at all, remove the actuator rod from the VNT lever. This will let you isolate and test the VNT lever's movement. If it's seized then you have to remove the turbo and clean the vanes. See the DIY articles linked at the top. When the vanes stick too much, the internal lever and ring wear into each other and stick/create play.

    How to remove and replace VNT actuator "wastegate can" on VW TDI or Audi TDI and adjust the rod
    It's easy to remove the actuator with the turbo on the car if you have a ratcheting wrench like this.....

    .....the rest of this article and detailed pictures are in the premium content forum in this post. Please join our community today and upgrade your account to premium: http://www.myturbodiesel.com/account/upgrades Thank you for your support!