Peugeot 408 Overheating and Coolant Leak

I had something similar with my 408. Check the control module connections. Could be a faulty plug or damaged cable.

Thanks! Where exactly is the control module located, and how involved is it to check the connections?

It's a pain to get to, honestly. The error sounds awfully familiar, diagnostic trouble code and all that. I'd bet it's the wiring. I wouldn't mess with it too much yourself unless you know what you're doing – could cause more damage. Take it to a shop; they'll find it quick.

Turns out you were spot on! Took it to the shop, and it was a defective cable to the control unit, just like you said. Cost me 95€ to fix. Thanks so much for the help!