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Discussion Starter #1
Hi, my 2006 A3 2.0 TDI 140 turbo won't boost - unless I remove the pipe that comes out of the vacuum reservoir - in which case it boosts well. I've spoken to local garages, several Audi technicians and turbo specialists and no one has been able to provide an answer as to why it will only boost when the vacuum reservoir pipe is removed. It will still go into limp mode randomly. MAF, MAP, EGR, ACTUATOR, ETC have all been replaced, and a smoke test showed no vacuum leak. EML has come on several times always showing underboost. If anyone can shed any light on this I'd be very grateful - thank you!
 

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First posts normally go in introductions else you could get a free fix and we never see you again!!!

Forum Rules and Guidelines

Any problems search TDI Wiki as that covers write ups and forum posts.

You need to get your motor scanned (preferably with VAG-COM\VCDS) for any error codes logged in the ecu and post them, that will save a lot of guessing and check systems out.
 

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OK thanks for that. This car has had a lot of people look at it, the only error code is 2099 Underboost. I've had no luck with local garages, Audi VW specialists and Audi master technicians, so I thought it might either just ring a bell with someone who found the same thing, or someone might be able to work it out. It's quite a specific and unusual situation so I thought someone might fancy a challenge! The key question is why does the turbo only boost when the vacuum pipe is removed from the vacuum reservoir? I'm interested in the process of working it out, not just in a fix. Happy days!
 
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Mine is a P0299 [below control limit] have done a vacuum test to find the diaphragm is faulty, have ordered a new one to replace it [ Tiguan VW 2.0 TDI 103KW Turbo Electronic Actuator wastegate ] its a V W so it will do all sort of weird sh--. I am working my way through the engine, 1 st one [throttle control] replaced [fixed], 2 nd P2015 [flap motor control] replaced with deisel geeks part, [fixed], 3 rd failure the one above, so I am waiting for a replacement. To see how the turbo actuator works go to youtube & enter VW 2.0 TDI 103KW Turbo Electronic Actuator wastegate & they will give you a run down of the system. Hope this is informative, sadly not a fix.
 

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Discussion Starter #5
Thanks very much for that - a new actuator has been fitted, but the video is really instructive so thanks for the link. We're going to take the turbo off next, it's pretty much the only part that hasn't been replaced and it does seem like the problem lies there. I'll post an update when this has been done.
 

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the only error code is 2099 Underboost
When posting errors you post the full code with letters, what was that scanned with?

This is a common code as I've said. Any problems search TDI Wiki as that covers write ups and forum posts.

VAG Error Code: 16683/15343/14914/11226/12896/7384/5171/5671/000665

EOBD II Error Code: P0299

Fault Location:
Boost Pressure Regulation - Control Range Not Reached/Low Boost

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Reduced Power Output.
Limp Mode.
Limp mode: What is it, what are the causes, and how to fix it for the Audi and VW TDI diesel turbo.

Hoses/Pipes incorrectly connected, disconnected or leaking.
Charger Pressure Control defective.
Turbocharger faulty.
Diverter Valve faulty.

Possible Solutions:
Check Hoses/Pipes to/between Components.
Check/Clean/Replace Charge Pressure Control.
Check Turbocharger.
Check Diverter Valve.

Special Notes:
If the Turbocharger is faulty due to mechanical/internal problems or the exhaust system is restricted (typically the Catalyst) this fault may be the end result.

Gasoline:
When found in 2.0l TFSI:
Check Boost Pressure Control Valve (N249) (Turbocharger Recirculating Valve) for cracked rubber diaphragm. A new/optimized Valve is available under Part # 06H-145-710-D (or newer).
Rest of World (RoW) vehicles see: Technical Product Information (TPI) 2016331 for details.
North American Region (NAR) vehicles see: Technical Service Bulletin (TSB) 01-07-70 or 2013392 for details.
When stored in conjunction with misfire codes and/or fuel trim faults see the notes associated with the following faults regarding Positive Crankcase Ventilation (PCV) failure: Crankcase Breather Valve
When found in Audi A4/S4/RS4/Cabriolet (8K): 2.0l (CAEB):
See Technical Product Information (TPI) 2031245/6 - turbocharger excessive waste-gate play.

Diesel:
When found in VW Golf/Jetta (1K): 2.0l CR-TDI (CBEA/CJAA):
Verify the mechanical part of the Exhaust Valve Control Module (J883) is not seized or binding.
When found in the 1.9 L TDI-PD (BLS):
Check vacuum supply from the vacuum reservoir located in the valve cover for leaks. Using a vacuum gauge, wiggle the valve cover and hose connections to check for a leak. The following photo was submitted from a customer working on a 2010 VW Caddy (2K chassis) with this vacuum reservoir problem.



EOBD II Error Code: P02CB


Fault Location:
Turbocharger/Supercharger 'B' - Underboost Condition

Possible Cause:
Wiring/Connector(s).
Manifold Absolute Pressure (MAP) Sensor (G71).
Turbocharger/Supercharger boost pressure sensor.
Turbocharger wastegate actuator.
Turbocharger.
Supercharger.
Mechanical fault.
Engine Control Module (ECM).

Possible Solutions:
Check/Replace all faulty Wiring/Connector(s).
Read Measuring Value Blocks (MVB).


As taken from my new Free EOBD II Error Codes software
 
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Have just had they turbo actuator replaced on my 2008 Tiguan TDI 2 Ltr by a V W trained mechanic who now works for himself, fixed the low boost ect but not the MIL which brings up the engine Mgt light, OK he had the latest plug & play diagnostic tool & informed me that to clear the MIL I would have to go to a VW dealer to get this done? Another mechanic who told me he was V W trained & had told me the same story when I originally was finding the problem.
So the question I am after is this true ? or do all V W trained people get programed to do this as part of their training. If there is another way of fixing the light I would like to know, with out having to fork out $ 150 for a test.
 
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