Peugeot 508 brake booster pressure sensor issue

It seems like a faulty brake booster pressure sensor could be the culprit, especially given the symptoms you're describing. I had a similar problem with my Volvo V70 a while back. Was the brake system perhaps bled incorrectly recently?

That's interesting. I actually did have the brakes bled a while ago. I didn't make the connection, but could this really cause the pressure sensor to fail? Is there a specific procedure to follow when bleeding the brakes on these systems?

Yes, an incorrect bleeding procedure can definitely damage the pressure sensor. It is highly sensitive. To be safe, I suggest taking it to a workshop. They should be able to diagnose and fix it properly.

You were right. I took it to a mechanic, and they confirmed it was the pressure sensor, likely damaged during the brake bleeding. The bill came to 90€.