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What I Had to Do With the Cheap Catalytic Converter
Here is the part I want people to really understand. With the cheap catalytic converter, the only way I was able to keep the check engine light off was by using a U-shaped oxygen sensor coupler. That coupler moves the O2 sensor out of the normal exhaust path so the Prius does not read the exhaust gases the same way.
That might make the check engine light stay off long enough for the monitors to run, but that does not mean the catalytic converter is right. It also does not mean the setup is legal or proper for smog. In fact, the need for that coupler is exactly what made me realize this was not the right catalytic converter to recommend.
Original AliExpress product image shown for reference only. I am not linking to it because I do not recommend this catalytic converter.
The factory O2 sensor location exists for a reason. If the sensor has to be moved out of the normal exhaust stream just to keep the car from throwing a catalyst efficiency code, then the catalytic converter is not doing the job the way it should.
I also learned that the visual inspection side matters. A smog technician can look underneath the car and see whether the catalytic converter has the proper markings. They can also see if the oxygen sensor has been modified with a spacer, extender, or U-shaped coupler. If they see that, it can be treated as a modified emissions system, and that is not something you want documented on your vehicle during a smog inspection.
So yes, I was able to make the cheap catalytic converter work in a very specific situation, but I would not recommend that route. It was stressful, inconvenient, and not the correct fix. The better answer is to buy the right catalytic converter the first time.
