Aftermaket exhaust, PO420 code? - Toyota Yaris Forums

Bluevitz-rs · 06-16-2016, 12:21 AM

B1S1 will bounce up and down and is in control of the AFR of the engine. B1S2 is only there to measure the output of the Cat. O2 sensors are slow compared to the newer AFR sensors used on new cars, so it bounces back and forth trying to maintain 14.7 AFR.

The B1S2 should NOT read the same as B1S1. That indicated that the Cat is not working. It should bounce up and down, but much slower and not hold a higher reading for to long.

I had trouble after building my Turbo system with P0420. I built all my own exhaust and used the stock Cat in the system. I knew it just wasn't getting hot enough, fast enough, so I just recently built and installed a restrictor plate just behind B1S2 to slow down flow and keep the Cat hot and I haven't had a code since.

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06-16-2016, 12:21 AM	#13
Bluevitz-rs 1NZ-6spd View User's Garage Drives: '05 6-Spd Vitz RS Join Date: Oct 2008 Location: Oshawa, Ontario, Canada Posts: 2,967	B1S1 will bounce up and down and is in control of the AFR of the engine. B1S2 is only there to measure the output of the Cat. O2 sensors are slow compared to the newer AFR sensors used on new cars, so it bounces back and forth trying to maintain 14.7 AFR. The B1S2 should NOT read the same as B1S1. That indicated that the Cat is not working. It should bounce up and down, but much slower and not hold a higher reading for to long. I had trouble after building my Turbo system with P0420. I built all my own exhaust and used the stock Cat in the system. I knew it just wasn't getting hot enough, fast enough, so I just recently built and installed a restrictor plate just behind B1S2 to slow down flow and keep the Cat hot and I haven't had a code since.