The node that you want to connect to should either have the oracle intelligent agent running.

you can check that through

lsnrctl dbsnmp_status;

if not start it

lsnrctl dbsnmp_start;


Now go to your OEM console and point to the nodes and right click and choose the discover node option.
When the discovery window pops up, specify your nodes name

xys.com or etc

That will discover the node. If it cannot then choose the manual radio and configure it manually.

Hope this would help.
Sam