Puma diesel generator fault

Sounds like an alternator issue, which is sometimes called a generator. Weak or flickering lights, combined with a battery light and starting problems, definitely points that way. Have you checked the serpentine belt to make sure it's properly tensioned and not slipping? A slipping belt can cause the alternator to underperform. Also, confirm your battery voltage is actually low. A bad battery can sometimes mimic alternator problems.

Serpentine belt looks okay, tension seems right. Battery voltage was a bit low, around 12.2V with the engine off. But even after charging it, the problem persists. Is it still likely the alternator even with a fully charged battery?

12.2V is on the low side for a resting battery, it should ideally be around 12.6V. However, if the symptoms persist even after a full charge, and you're getting a generator fault code, it's highly probable the alternator is failing internally. Could be the voltage regulator or the rectifier. I'd advise getting it professionally diagnosed and replaced, as a faulty charging system can lead to other electrical issues.

Thanks for the advice. Took it to the workshop, and you were right – faulty generator. Repair cost was 960€. Replaced the generator, and all issues are now resolved.