John Welch.

I recently swapped my 955T for a 957T and I have a low boost situation. I can't be certain that the boost ever went that high, but right now, I'm only achieve .4 bar.

I scanned for codes but there weren't any.

I would think if there was a leak, there would be a code.

Could this be a diverter valve issue?

nodoors

Could be or seal(s) in the charge pipes.

John Welch.

I guess I should do a boost leak test before buying any parts.

TomF

Try this before you spend a lot of time on other ideas. Get out on an open road, put the car in Sport mode, turn off PSM and manually shift up to third gear as soon as it will let you. Then floor it. You should see the boost guage climb to .7 - .8 bars very rapidly. I find that in normal mode or sport mode, I rarely see above .4-.5.

Cheers,
TomF