P0299: Limit exceeded, please comment on logs

There's a lot of information available on this topic, but I've reached a point where it would be really helpful if someone with more experience could take a look at it.

Code:

Adresse 01: Motorelektronik (CBA)       Labeldatei: DRV\03L-906-022-CBA.clb    Teilenummer SW: 03L 906 022 BL    HW: 03L 907 309    Bauteil: R4 2.0l TDI G001SG  9980     Revision: --H01---    Seriennummer: VWZCZ000000000    Codierung: 0000072    Betriebsnr.: WSC 84224 792 403624    VCID: 70EB80386374450F3C-8024    VINID: 9E69EAAAA0D3A88542040249209F3A3CA3 1 Fehler gefunden: 000665 - Ladedruckregelung                P0299 - 000 - Regelgrenze unterschritten - Warnleuchte EIN              Umgebungsbedingungen:                     Fehlerstatus: 11100000                     Fehlerpriorität: 2                     Fehlerhäufigkeit: 3                     Verlernzähler: 255                     Kilometerstand: 167631 km                     Zeitangabe: 0                     Datum: 2022.09.25                     Zeit: 14:40:08              Umgebungsbedingungen:                     Drehzahl: 2300 /min                     Geschwindigkeit: 119.0 km/h                     Last: 76.5 %                     Druck: 2346.0 mbar                     Druck: 1917.6 mbar                     Lambda: 92.3 %                     Lambda: 46.6 % Readiness: 1 1 0 0 0

Error image
Passat 3C, year 2008, 167,000 km, engine code CBAB, 140 hp, manual transmission.
Boost pressure control P0299 - 000 - Regulation limit exceeded.
Occasionally, the engine warning light comes on and the car goes into limp mode, usually when accelerating in 6th gear around 100 km/h. So far, it has only happened when the engine is fully warmed up, but it has occurred multiple times and is reproducible.



Analysis
- N75 valve removed and measured. The relay is working, but doesn't seem to be sealing properly. Unsure due to lack of comparison/experience - replacement obtained.
- Two measurement runs (MWB 8, 10, 11) were performed with the old and new N75 control valve. The error occurs even with the new part. My interpretation: The actual boost pressure lags significantly behind the target boost pressure (Diagrams 1+2), but it does eventually build up. Acceleration is definitely present at higher speeds.
- Test drive MWB 34: It is noticeable that the value for the boost pressure control (feedback) does not change.
- Performed using VCDs under "Engine Electronics/Basic Settings/ 'Check of Turbocharger Pressure Control'".
- When the control system is turned on or off, the pressure reading does not change.
- However, the measured value directly at the output of the sensor changes between 3.5V and 2.6V.
- In addition, movement of the pushrod can be observed. The amount of displacement could be approximately 1 centimeter.
Questions
It seems like the VTG adjustment is working, but the position feedback is present at the sensor, but not reaching the control unit. Is this interpreted correctly?

Could a cable fault be the cause? I would rather expect a false alarm indicating an implausible measurement value.

What other causes could be possible besides a faulty control unit?
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Hello,

With no boost pressure control valve, the actual boost pressure will not reach the desired boost pressure.

If the VTG pressure sensor makes a crisp, popping sound, the most likely cause is a leak in the charge air duct. It is also recognizable by very high LMM (mass flow meter) values.
Leaks can be identified by oily spots.

Another possibility is that the exhaust turbine is not being driven due to a faulty exhaust temperature sensor.

Best regards, Rainer.

Hello,
Thank you for the quick response so late at night. There's oil on the left side of the LLK; I'll try to wipe it off. That fits with the observation that the LD (likely referring to a specific measurement or value) doesn't change during the LD test and doesn't reach its normal level.
Do you have an explanation for why the value for "boost pressure control (feedback)" in module MWB 34 doesn't change even though the push rod is moving? I would just like to understand it. Does this value in VCDS not indicate the "potentiometer position within the module"?
Sure, here's the translation:

"Best regards,
Thomas"

Hi,

No change in MWB34 despite movement: I have no idea, sorry. The feedback signal may not be used.

Best regards, Rainer.

It's been a while, but here's the cause (I hate it when threads just end like that ).
It was the vacuum cylinder for the VTG adjustment. I got a hand pump, and the rod barely moved. What I saw during the first test, assuming the adjustment was correct, I have no idea; it was just very difficult to see clearly.
New can, new inspection, everything's good.

Thank you for the feedback!