DS3 transmission fault radiator pressure

Sounds rough! I had similar symptoms on my DS3, though it wasn't exactly the same. Was your cooling fan running constantly? And have you checked for any coolant leaks around the radiator or the pressure sensor itself? Could be a faulty sensor giving bad readings to the transmission control unit.

Thanks! The cooling fan seems to be running more than usual, now that you mention it. Where exactly is the pressure sensor located, and how did you figure out it was the sensor? Any tips before I start ripping things apart?

Okay, running fan is a big clue. Honestly, I didn't figure it out myself. The symptoms were similar, but I took it to a workshop. They traced it to a dodgy connection on the radiator pressure sensor. I'd suggest doing the same, especially if you aren't super confident. Better safe than sorry, right?

You're right. I took it in. Turns out it WAS a defective cable connection on the radiator pressure sensor, just like you said. Cost 95€ to fix. Thanks for the advice!