Peugeot 607 Transmission Slipping Grinding

Whoa, that sounds rough! I had something similar happen with my 607, although maybe not quite as dramatic. Did you notice any engine surge or weird RPM fluctuations along with the slipping? For me, it felt like the car couldn't decide what gear it wanted to be in. I'm wondering if it's the same gremlin causing your issues.

Engine surge, you say? Now that you mention it, there IS a slight surge sometimes, almost like it's hesitating. It's subtle, so I didn't immediately connect it. Is that lock-up clutch known to cause that? Did you also hear grinding noises?

The surge and hesitation are what made me suspect the lock-up clutch in the first place. The grinding noise is concerning though, I didn't have that. It's entirely possible the defective converter has caused additional damage in your case. I'd strongly recommend getting it checked out by a reputable workshop that knows these transmissions. They can properly diagnose the extent of the damage. It could save you even bigger headaches down the road. I had to get mine replaced; was not cheap!

Thanks a million for the insight! I suspected it was heading toward a costly repair. I took your advice and brought it to my trusted mechanic. Turns out the automatic transmission converter was indeed defective, just as the error code suggested. The final bill came to 2120€ for the repair. Ouch! But at least it's running smoothly again. Your comments helped me mentally prepare for the diagnosis.