GLA Diesel engine performance issue resolution

Sounds familiar. I had a similar issue with my GLA check engine light and power loss. The whistling and hissing sounds definitely point towards a boost leak somewhere in the turbo system. The boost pressure actuator fault is a common culprit. Have you checked the actuator valve itself for any obvious signs of damage or wear? When you say 'electrical bypass valve defective', are you referring to the diverter valve?

Regarding the electrical bypass valve, I was indeed referring to the diverter valve. I have not yet conducted a thorough inspection of the actuator valve for physical damage. Could you elaborate on the specific areas of the actuator valve that are most susceptible to failure or wear? Any further guidance on diagnosing a boost leak within the turbo system would also be greatly appreciated.

Okay, got it. The diverter valve on these can get sticky or even crack over time, leading to a boost leak. Also the hoses around the turbo can become brittle and leak. Given the symptoms and the actuator fault code, it's likely related. Honestly, with those kilometers, and without specialized tools, pinpointing the exact location of the leak can be tricky. I ended up taking mine to a workshop. They were able to diagnose it quickly. If you don't have experience with turbo systems, I'd recommend getting it checked out. It might save you time and money in the long run.

I appreciate your advice. Based on your recommendation, I have decided to consult a qualified mechanic for a professional diagnosis. The workshop confirmed the defective actuator valve was the source of the boost leak. The repair, including parts and labor, amounted to approximately 250€. Thank you again for your assistance.