Megane transmission error

That sounds rough! The error code does point towards a radiator/oil cooler issue. When was the last time you checked your coolant levels? Have you noticed any leaks, maybe around the radiator or under the car after it's been parked for a while? It could also be something as simple as a faulty sensor, but the slipping and grinding sounds like you should definitely get it checked out soon.

Thanks for the reply! I checked the coolant levels and they seem okay, haven't noticed any visible leaks either. How would I go about checking the sensors? Is there a specific one related to the radiator oil pressure that I should be looking at?

Given that you haven't seen any leaks and the coolant level is fine, the issue might indeed be with the sensor or its wiring. However, because you're experiencing those shifting problems, I would recommend taking it to a workshop. They can properly diagnose the exact cause of the error – it could be a defective cable or plug connection. The cost to repair is about 95€.

Thanks for the advice! Took it to a local shop, and you were spot on! It was indeed a defective cable connection for the radiator oil pressure sensor. They fixed it up, cleared the codes, and now it's shifting smoothly again. Really appreciate the help!