Don't know much about the secondary air pump system on the hawks but it looks like an emissions thing introduced on the 2.5's - basically sends fresh air direct into the exhaust for 30 seconds on cold start to get the cats to work faster.
Had a google and some of these links might be useful reading...seems to be an expensive fix if you do it properly, but there's an option to blank them off rather than replace (if yours is at fault) and then remap.
https://www.scoobynet.com/general-te...-air-pump.html
https://www.scoobynet.com/general-te...on-06-wrx.html
http://www.subaru4you.co.uk/engine/secondaryair.shtml
http://uk.subaruownersclub.com/forum...ir-pump-fault/
Doesn't sound a cheap & simple fix unfortunately - good luck with it!
