I have Volvo V50 T5 model year -05 (automatic) and mileage was back then when I bought the vehicle around 90000 / 146 000 km. Vehicle was in good condition but after one month ago I got "Reduced Engine Performance" message to my dashboard. I used OBD-reader and it gave error code P0101 which is Mass air flow sensor error. I read some forums that It could be only dirty airfilter so I bought new one. Then I released the error code, because vehicle seems to have power issues when code was on and fuel economy went bad.
It took about 6-7 months until I got same "Reduced Engine Performance" message to dashboard. OBD gave same error code. This time I bought entirely whole MAF-sensor unit around 70-80 euros and It was easy fix. Then I reseted the code.
Now It took around one month and again same "Reduced Engine Performance" came to dashboard. Now OBD didn't gave any error codes. Then I was searching online some clues and I bought new fuel pressure sensor around 40 euros. Swap was pretty easy and now after around 930 miles / 1500km Volvo is doing fine without messages in dashboard.
In summary "Reduced Engine Performance" can mean many diffrent things. I think I had two diffrent problems going on. One was the MAF and the other was fuel pressure sensor and only MAF gave error code to the OBD reader but still those gave same dashboard message. I hope this will help someone
