First time poster, I drive a 2015 Mercedes C300 (W205).

The car keeps going in limp mode, a couple issues have come up:
P04DB79 - The crankcase ventilation system is interrupted. The mechanical connection has failed.
my guess on this one is that the valves would have worn down and need to be replaced? I remember this being an issue on the 2014 C250. The rubber would become brittle and the vacuum would start failing.

P029921 - The boost pressure of turbocharger 1 is too low. The signal amplitude is less than the minimum amplitude.
I believe this is the issue which is making the car go in limp mode. The only thing I can come up with here looking at other models is the high pressure fuel pump?

Any advice is welcome, if you need any more info please let me know.

 

vacuum leak

 

try checking the hoses for the intercooler or even vacuum lines that connect to the turbo.

 

My service center let me know the turbo waste gate is not holding vacuum and recommended me to replace the turbo for $4900.

Is there really no other fix to this other than changing out the entire turbo?

 

Did you previously suffer from the "P052E : Positive Crankcase Ventilation Regulator Valve Performance" issue? If this isn't addressed in a timely fashion pressure builds up in the engine and causes a leak.

 

The most common problem, which we found after replacing a bunch of sensors, etc.

The problem was bad wastegate vacuum diaphragm.
When wastegate vacuum diaphragm is defective or broken, will leave the wastegate valve wide open

Easy way to test. Using vacuum pump put onto vaccum and if the wastegate valve does not hold closed and, vacuum does not drop then this is your problem.

This is very common problem due to the fact that the diaphragm is rubber and it is mounted on top of the turbo connected to the Exhaust manifold and this area gets very hot

 

As mentioned by another bro, check the actuator for vacuum leak....
I have seen before that the turbo wastegate flapper doesn't seal well and the turbo needs to be replaced, but we usually try the cheaper options first.

Instead of swapping out the turbo, you can swap 2 things first.
1) try replacing with a new actuator first - A2740904200
2) try replacing with a new boost solenoid. - A0101531328

Oh, and you want to check for other possible leaks first; at the charge pipe connections, the vacuum rubber hoses, etc.