Code120308

This code is telling you that the actual boost pressure and the commanded boost pressure are not the same, so it interprets this as an issue and limits the boost so that there is no damage.

There are a number of things that can cause this, so we need to start with checking for a vacuum leak to find out if we are losing pressure somewhere.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If there are no leaks, then we need to check the exhaust flap and make sure it is sealing as that is the next most common cause of this.

Once we run through this, we can take the next steps but that would be smoke testing the charged air side of the system to see if we have a leak in this system.

The flap is there to control exhaust flow to the turbo during low or no boost needed situations.

I am attaching more details about it below. The replacement of the actuator is below the previous post.

However, if this is hanging open or closed then it will cause the boost to be different than commanded and set this code.

I would access it and check for carbon build up as that will cause it to stick.

Take a look at this info below.