Volvo Repair: Air pump failure, solenoid valve, scan tool

Question
I had check ingine light with codes for air pump on 1997 850 volvo. How can I found out if I need to replace just air pump relay with solenoid valve or I need also to put a new air pump?  

Answer
the way I do it is with the volvo scan tool I operate the pump and see if the relay works and I can hear the pump.if I hear the relay but no pump the pump is bad.problem is both usually get water in them due to where they are located.you would need to try checking power to the relay and ground to the relay.