Peugeot Expert Reduced Engine Power

That sounds frustrating! I had a similar issue with my old Renault Megane, although it was a petrol engine. Reduced power and error codes pointing to the ECU. An ECU, or engine control unit, is basically the car's computer, controlling all aspects of engine performance. Did you try a system reset? Sometimes that clears things up temporarily, but it sounds like the relay is the core problem. Where did you get the info about the relay?

Thanks for the reply. A system reset hasn't helped, unfortunately. The relay diagnosis came from a friend who's a mechanic. He suggested it might be intermittently failing, causing the ECU to throw errors. Is it possible to replace the relay myself, or is it something only a workshop can do?

Ok, if a system reset didn't do the trick, then the error is still present, meaning the problem might be bigger than just some temporary glitch. I wouldn't advise messing with the ECU or relays yourself unless you really know what you're doing, you could make things worse. In my case with the Megane, I ended up taking it to a workshop, and they were able to pinpoint a similar power supply issue affecting the ECU. Probably best to let professionals handle it with the right equipment.

Thanks, I appreciate the advice. I took it to a workshop, and you were right. It was indeed the main relay, which they replaced. Cost me about 120€, but at least the van is running smoothly again.