Review on Enhanced Performance: Oxygen Sensor Downstream 234 4623 Pontiac for Efficient Fuel Combustion by Mark Cannon

Designed to replace the OEM sensor with over 200,000 miles (but otherwise works fine) as part of the catalytic converter replacement to clean up 2006 year Prius for the smog- prepare test. . I ended up returning this and kept using the original for now (again - cat, original upstream and downstream O2 seem to work together - no codes). After a short drive, the Autel AL319 I/M Readiness Scanner shows a Pd (pending) DTC. The code scan returns P0420 (Catalyst system efficiency below threshold). After a little longer driving, DTC Pd becomes a DTC followed by a check engine light and usually another code (P0138 - O2 Circuit High Voltage). Maybe that's a faulty part, or maybe they're too generic for the picky Prius Gen2; I'll never know, but at least I was able to return it for a refund.