Peugeot Boxer power loss

That sounds frustrating! I had a similar issue with my Opel Insignia a few years back. Reduced power, flickering lights, and a cranky start. It turned out to be a defective alternator. Were you able to check the voltage output of your alternator? A significant drop would certainly point towards it being the culprit.

Voltage output, eh? I haven't checked that yet. Where exactly would I measure that, and what's a normal reading supposed to be? Just trying to pinpoint this before I start ripping things apart unnecessarily.

You can check the voltage directly at the alternator terminals with a multimeter while the engine is running. A healthy alternator should be putting out around 13.5 to 14.5 volts. If it's significantly lower, or fluctuating wildly, it's a pretty solid indicator that it needs replacing. Given all your symptoms, including that error code, it might be best to visit a workshop for a proper diagnostic procedure.

Thanks for the advice. I ended up taking it to a shop and they confirmed it was indeed the generator. Cost me about 960€ for the replacement, but at least it's running smoothly again. Thanks for pointing me in the right direction!