The PO410 code is usually set by the AIR system. There is a set of one-way AIR valves that keeps exhaust in the manifold from going back up the AIR injection lines, toward the pump. The ECM tests the function of the air system by checking for fluctuations in the 02 sensors when the AIR pump is on (the sensors will pick up on the extra fresh air entering the exhaust stream and fluctuate "lean". When these valves get caked with exhaust crap over time, they get plugged up and dont let as much air through, or sometimes they get stuck shut and dont let any of this air through at all. So.....the pump cycles on, the 02 sensor voltage dosen't change the required minumum amount to signify a "leaning" of the exhaust from the Air injection, and the code sets. You can try cleaning the AIR valves, or just install new ones. I think they are pretty cheap, and the same valves that GM has uses since the 80's im pretty sure. Hope that helps