Peugeot 407 Boost Pressure Fault

Those symptoms definitely point to a boost issue. Have you noticed any unusual noises, like a hissing sound, when the turbo is supposed to be spooling up? A pressure drop could also be caused by a leak in the intercooler piping. Does the engine feel particularly sluggish at low RPMs?

I have not detected any hissing sounds. The engine is indeed sluggish at low RPMs, exhibiting noticeable turbo lag. Could a defective vacuum switching valve also cause these issues, in addition to a faulty pressure sensor?

A vacuum switching valve issue is certainly plausible and could mimic the symptoms of a faulty pressure sensor. Considering the turbo lag and lack of hissing, it might be the more likely culprit. While diagnosing it yourself is possible, a workshop visit might save you time and potential misdiagnosis.

Based on your assessment, I took the vehicle to a workshop. The diagnostic confirmed a defect in the vacuum switching valve. The repair cost 140€, resolving the boost pressure control fault.