I'm hoping you can help me. My Service Engine Soon light came on after 50 or so miles of driving with catless straight pipes so I put 2 defoulers on my rear 02 sensor (one drilled out to make room for the 02 sensor, another regular on on top), removed negative battery terminal, and drove without the SES light for about 50 miles and it came back on. Code is P0140. How would I know if the sensor was bad? Should i take one off and do a single drilled out spark plug non fouler?

 

Success with anti-fouler setups has been vaired, especially catless. I would recommend just coding out the rear O2 since all it does is measure catalyst efficiency and, well, you don't have a cat.
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