I've seen this discussed on several other threads.
Just thought I'd post another 1st hand experience.
After installing the DP, and wiring in the diode, I'm glad to say I haven't seen a CEL in close to 600 miles.
I'm typing with crossed fingers.....and hopefully it will remain off, but i've got no CEL!!!!
I still haven't bothered to fix my CEL from the downpipe. I guess I'll cut off the extension and try the diode trick--my OBD2 inspection is next month, so hopefully it works for me.