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I keep getting P0420 depending on the gas I use. Now it comes on every 200 miles or so. I replaced both B1S1 and B1S2 because they are old. B1S1 is original with 300k miles.
I just installed the dual plug anti foulers and time will tell. I monitored the O2 sensors on my 1 hr commute. It def reacted slower than bank 2 and usually stayed between 0.1-0.3

Update. After 400 miles since installing the device, no p0420 code and I passed the emissions test this morning.


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