in August I had 4 times P0299- Underboost. Car goes to limp mode with Error: Drive System. Turning car off and on deletes the message and car drives normally after that.I did 1000km after the last error with no problem . I asked VW workshop to do diagnostics and they said that its a actuator broken and that I need new turbo as only actuator cant be replaced. I logged live data in CarScanner Pro for Turbo position with variable geometry request and actual and there are no differences. Did anyone have that problem and did you had to change whole turbo( Prices is insane they are asking for 4000 euros)

Turbine overboost in most cases is indeed related to stuck geometry (vanes) or a malfunction of the actuator (its vacuum/electronic parts or the N75 control valve). Since your car is under warranty, your main goal is to correctly record this defect for the official dealer so they don't dismiss it as an "accidental error."

On a 2020 Skoda Octavia 2.0 TDI (likely an EA288 or EA288 evo engine), the engine control unit (ECU) uses the modern UDS protocol. In Car Scanner, these sensors (PIDs) are well-defined.

1. Which Sensors (PIDs) to Select in Car Scanner:

Connect to the car, select the correct connection profile (Skoda OBD-II / MQB), go to the "Live Data / Graphs" section, and select these specific parameters:

• Engine RPM: Engine RPM (rpm).

• Gear: Target Gear or Current Gear (crucial to see the exact moment of the DSG shift).

• Target Boost (What the computer requests): Charge pressure: specified value (measured in hPa or mbar).

• Actual Boost (What the turbo actually delivers): Charge pressure: actual value (in hPa or mbar).

• Actuator Position (Crucial for the dealer): Positioner for charge pressure actuator: acknowledgment or Activation of boost pressure control valve (measured in %).

💡 Understanding the Numbers: At idle, the sensor shows atmospheric pressure, which is around 1000 hPa (1 bar). Under full acceleration, the target boost will be around 2500–2600 hPa. If the actual boost spikes to 2900–3000+ hPa, that is your overboost.

2. How to Correctly Record the Log (Driver's Guide):

You must record the log under high engine load to force the turbo to peak boost.

1. Find a safe, straight stretch of road (ideally a highway or a slight uphill slope).

2. Move the DSG gear selector into Manual mode (M).

3. Engage 3rd or 4th gear.

4. Slow down until your engine speed drops to 1500 RPM.

5. Press the "Record" (Play) button in Car Scanner.

6. Press the accelerator pedal 100% to the floor (Wide Open Throttle). Do not press it past the kick-down click, so the DSG doesn't automatically force a downshift.

7. Hold the pedal down until the engine reaches 3800–4000 RPM.

8. At this point, shift up to the next gear (e.g., from 3rd to 4th) while keeping your foot heavily on the gas, and continue driving for another 3–4 seconds.

9. Stop the recording.

3. What to Look For in the Log for Your Warranty Claim:

Export the data as a CSV file or look at the graph in the app. The smoking gun for a faulty VNT geometry/actuator on a 2.0 TDI will look like this:

• As RPM rises, the Specified Boost stabilizes (e.g., at 2500 mbar).

• The Actual Boost shoots way past it up to 2900+ mbar.

• The Actuator Position (%) drops to its minimum threshold. This proves the ECU is trying its hardest to open the geometry and dump the pressure, but the actual pressure won't drop because the mechanism is physically jammed.

• Immediately after this layout occurs, the car will throw a glow plug light (coil) or Check Engine light on the dashboard and enter Limp Mode.

Take this graph or CSV to your official dealer. They will be forced to run a guided actuator test on their ODIS diagnostic system and will most likely replace the turbocharger or the electronic actuator under warranty.

Once you record the log, let me know:

• Were you able to capture the pressure spike on the graph?

• What specific error code (e.g., P0234) did Car Scanner read when it happened?

Feel free to share the peak values (specified vs. actual) here for a quick analysis!

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