My car is a Mercedes-Benz CLA250 2020 model year, and the turbo booster error P029921 has been confirmed. The symptom is that the boost does not go up at some point while the turbo booster works, and when the engine is reset, the turbo boost rises again. And on the uphill road, there is not enough strength, so it is impossible to climb on a steep incline.

M260 engine was used in my vehicle

I also replaced the electronic turbo actuator, but the symptoms are the same