2005 SER SES Light Still on after Pre-Cat replacement

2005 Altima SER with 98K. Dealer told me my rear pre-cat was plugged and was causing the rattle in engine and SES light in my car. Replaced it (old pre-cat was very bad) but SES light still keeps coming on. Rattle is now gone. There are about 5-O2 Sensors in this car. The EGR Valve is, of course, integrated and intricate. Anyone have this similar issue? What can I check first to start eliminating?

Thanks

Any idea what code is stored for the C.E. light? Is the rattle from the engine and does it change with RPM?

Was the CEL reset & cleared after the new cat?
No - If the problem is resolved, it will clear it self after the drive cycle.
Yes - You got other problems, we need DTC's to analyze problem.

Almost any Auto store will pull codes for free, but don't buy any parts yet.

Write down any other symptoms:
Fuel economy
performance issues