Check engine light with code P0139 on 2006 Acura RSX

Would a secondary O2 sensor see a race header as a faulty cat?
My check engine light is on with a code P0139. I have checked the wiring, replaced the O2 sensor and put a non fouler/ check engine light eliminator in the secondary O2 bung.

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1 answer 1 comment
SHOULDN"T SEE IT LIKE THAT BUT YOUNEVER KNOW ON CARS. ARE YOU ABLE TO READ O2 ACTIVITY?
I can read the secondary O2 sensor voltage and it stays around. 5 volts