Post-cat O2 sensors

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I will put this out there for your consideration.

The pre cat sensors do the heavy lifting for the fuel injection system, they set the overall rich/lean mixture for the engine. If a pre-cat sensor was to fail on my car I would replace both.

The post cat sensors are only to confirm that the cats are working. They are not nearly as important as the pre cat sensors. I would replace them one at the time.

Also the only thing that makes it a "Porsche" O2 sensor is the plug (connector). They are bog standard Bosch thimble type O2 sensors and if you are willing to do some soldering you can buy them for $39 but you have to solder your Porsche plug to the wires.