Peugeot 408 Brake Booster Pressure Sensor Failure

Incorrect bleeding of the brake system can indeed cause issues with the brake booster pressure sensor. Air in the system can lead to erratic pressure readings and subsequent sensor failure. Has the brake system been recently bled?

The system was bled recently. Is there any way to confirm that the sensor is the actual issue and not just a symptom of air in the lines?

Confirming the sensor definitively requires advanced diagnostic tools to measure its output under varying pressure conditions. Given the recent bleed, and the error codes, it is highly probable the sensor has failed. I recommend a workshop visit.

Understood. I took it to a workshop; the brake booster pressure sensor was indeed faulty due to the recent bleed. Replacement cost 90€. Thanks for the advice.