S90 Reduced Engine Power

Sounds familiar. I had similar issues with my S90. Check your generator, or as some call it, the alternator. Seems like your charging system might be failing. That could explain the weak lights, poor starting, and the engine power reduction. If the generator isn't charging the battery properly, the car's electronics will act up.

Thanks for the quick reply! So, if it's the generator, is there anything I can check myself before taking it to a shop? Like, could it be a fuse or something simple like that? Or maybe the starter motor?

A fuse is possible, but unlikely given all the symptoms. A faulty starter motor would usually just cause starting problems, not the reduced engine power while driving. Honestly, with those symptoms pointing to the generator, it's probably best to get it checked professionally. A defective generator is most likely your problem.

Okay, thanks for the advice! I took it to the shop, and you were right, it was the generator. Cost me 960€ to replace. Appreciate the help!