Computer problem
1996 Volvo 850 Front Wheel Drive Automatic 70000 miles

When I check my DTC codes with my reader I get P0410 Secondary Air Injection System. While the Check Engine Light (CEL) is on the Fuel System is running in open loop and things look fine, but when I erase the DTC, turning the CEL off the fuel system then goes into closed loop and I get a "fault with at least one oxygen sensor". There are two oxygen sensors (pre and post cat) and I just replaced both of them with $100 "Walker" Oxygen Sensors. I have also tested and found to be working my Air Pump, Relay, and SAS Valve(Air Pump Check Valve). I don't think that a ground signal is ever sent to the air pump to turn it on during normal operation, but I can ground the relay and turn the pump on by applying a ground wire myself. I can't figure it out and it's very frustrating, any help would be greatly appreciated. Thank you very much.