Peugeot 3008 Transmission Oil Pressure Sensor Fault

Sounds like it could be a gearbox oil issue. The emergency mode, slipping, and grinding are all signs. Is it similar to when you run low on engine oil - the whole thing starts protesting? Have you checked the oil level? If it's low, there's likely a leak somewhere.

I haven't checked the level yet. Where exactly is the fill point, and is there a dipstick? Or do I need some special tool?

Usually, there isn't a dipstick on these newer gearboxes. The fill point is often a plug on the side of the transmission. Checking it can be a bit fiddly and messy; best to get it checked by a workshop. It really does sound like low oil, and continuing to drive it like this will likely make the grinding worse. Like running an engine without enough oil; it seizes up eventually!

Thanks, I appreciate the help. You were spot on. Took it to the shop, and the oil level was indeed low. They topped it off and fixed a small leak. Cost me 365€, but worth it to avoid further damage.