Traveller Turbo Whistle Power Loss

Sounds like you're on the right track with the turbo system being the culprit. That whistling/hissing combined with power loss is a classic symptom. Does the whistling change pitch with engine RPM? I'd check all the hoses and intercooler connections for obvious leaks first. Have you tried scanning the OBD2 port for specific error codes? That could narrow it down further.

Thanks for the quick response! Yeah, the whistling definitely gets louder and higher pitched as the RPMs increase. I visually inspected the hoses, and nothing immediately jumps out, but I'll double-check all the connections more thoroughly. I did get a code reader on it, and it's flagging a 'boost pressure actuator fault'. Does that point to the electrical bypass valve being defective?

A boost pressure actuator fault code definitely suggests a problem with the actuator itself or its control circuit. While it could be wiring, a defective electrical bypass valve is a strong possibility, especially with those symptoms. It's probably best to get it looked at by a workshop. Trying to replace the part yourself might cause further damage without proper diagnostics.

Thanks for the help! I took it to a local garage, and they confirmed it was indeed the electrical bypass valve. They replaced it, and the total repair cost came to around 250€. The Traveller is back to its old self now, boosting like new! Really appreciate the insights.