Cummins ISX 15 2250

[Garfeild]

I have a 2012 386 Peterbilt with an ISX 15 2250. the engine light came on Friday the display showed boost pressure, I hooked it to insite and it is showing an active code of 0123 and an inactive code of 0691. I got it home and it never derated on me I could hear the turbo working but not as loud as usual but my manifold pressure gauge is at 0. Not a mechanic but trying to learn to fix things myself. Not real sure if it would be a sensor problem or if it might be the turbo. Can anyone give me some suggestions on where to start please?