2012 V40D2 information message.
 

I have had the message "reduced engine performance" come up in the dashboard display, this seems to be intermittent. Can anyone advise please.

The only way to tell what’s wrong is via diagnostics. This error could be multiple things & its purely guessing without plugging the car into diagnostic equipment.

You need to go to a garage, preferably a Volvo one with the correct equipment to diagnose the fault.