"Decreased Engine Performance" message?
 

Car is a 2006 V50, T5 AWD, coming up on 90,000 miles, regularly serviced and maintained.

About every 5,000 miles, for the last 25,000 or so, I get the "Decreased Engine Performance" message. It's a decrease in performance that really isn't noticeable during ordinary cruise or casual acceleration but is definitely noticeable under hard acceleration.

When I get it, I dump a pint of Techron or Ventil Sauber into a tank of gas and it seems to go away for another 5,000 miles.

Is there a more permanent fix for this condition? Some people have said removing and cleaning the MAF sensor will do it.

Need the codes read to have any idea.

It's not throwing a code. No check-engine light, just the "decreased engine performance" message.

There are codes. Maybe not ones a generic code reader can read, but they are there.

Diagnosis is free at the dealer, so that might be your best bet if you have one near by.

I had a friend of mine that got the same message. He also had no codes and no check engine light on.........get ready for this .....it was a weak battery. Don't ask why but we tested the battery and it was only putting out 11.8-12 volts max even after being on a charger over night. So he swapped out the battery and has never seen that issue since. I am sure the battery was dropping below the 11.8 to trigger the message but the battery started the car just fine and showed no signs of problems so when people say volvos are finicky about having good batteries I can see why. Not sure if this is your problem, but you may want to check your battery and see if its just below the threshold because that can be it something this simple.