I think the first thing to check would be your OBD dongle. I'm quite sure if all the boost you can achieve is 5psi there definitely would be a code thrown. I also think it would have to be the bypass valve if something is not working properly.
No got to be something there are no codes. That's going to be because its running within operating tolerances, just not correctly. I checked for leaks and could not find any. My obd says it ok just no boost past 5psi. Throttle position sensor is working.
The turbo is the sole producer of boost, and exhaust pressure is what drives the turbo. There is no other control for the turbo. You step on the throttle, which produces increased combustion/gasses spinning up the turbo. It's that simple. If the engine rpm increases the turbo spins up.
Well ok that's embarrassing 😳. The loss of boost... well I discovered the intercooler pipe clamp broke. So the pipe slipped about half way off just enough to give me 5psi anything over that and pressure escaped though the faulty seal.
This is for Ricky your right the boost is driven completely off exhaust. But what actually controls the amount of boost you get us this sensor attached by some vac lines. Since I was getting some boost I figured maybe moisture or a short. The boost was there but it seemed like nothing was controlling it anymore.
I had just finished doing a complete bottom end rebuild bearings, connecting rods, pistons, and all the gaskets. I also went and did a valve job since I already had the motor torn apart in my shop. I never had this happen before.