I don't have the 400, so I can't answer that question with authority. Even more so, considering I thought the 400 pedal was a dedicated wah/volume pedal. I didn't know it was an expression pedal capable of other functions.
However...
On other units, such as the ones I own, you need to adjust the "mix" volume.
You want to listen to a 100% wet signal. Anything less will allow the dry signal through.
Again, I don't know if this applies to the 400, but....
You also need to know placement in the signal chain. If you have your pitch on the left, it won't change what you hear on the right.