P1404 Cadillac - Deville

Question

Need to pass IL emissions test.

I have a Deville with 200k miles on it. And am having a P1404 with SES lit trouble code, but occasionally it only shows as historical. Have replaced EGR valve, TPS, and Cadillac Dealer hasn't solved the problem yet. I had water pump housing (and pump) replaced 3 months back and EGR mounts near or on this housing (if I recall), not sure where or how to clean the passages but willing to do it if a method is suggested.

Also, other trouble codes have appears on occasion, and I think the codes may all be in common with one of the PCM's 5volt rails. None of those code are current, only the P1404.

Suggestions on how to proceed? Any way to know if there if there is a technical bulletin on reprogramming the PCM (short of possible dealer replacement at large expense).

Thanks for your review.