Peugeot 408 Glow Plug Problem

Sounds like classic glow plug failure! Is the engine light on too? Any rough idle, especially on cold starts? Defective glow plugs can definitely cause those symptoms, plus decreased fuel efficiency.

Yes, the engine light is on. There's a slight rough idle on cold starts too. Fuel efficiency seems marginally impacted. Could it be anything else besides the glow plugs, considering the symptoms?

With those symptoms and the error code, it's highly likely to be the glow plugs. Given the mileage, it's not unexpected. You'll probably need to get them replaced. It may be worth going to a workshop and get the issue confirmed.

Thanks for confirming my suspicions. Took it to the workshop, and you were spot on. Glow plugs were indeed the culprit. Repair cost came to 440€. Replaced them all, and the car is running smoothly again.