downstream o2 compatibility
 

Is any 4 wire universal sensor acceptable to replace the downstream o2 sensors? They are super cheap on eBay, and I am not concerned with how long they will last.

I wouldn't buy a universal one. Why not buy one that already has the plug on? You can get different brand name ones at a good price here:RockAuto Parts Catalog

Because when you can buy two for less than the price of one, it's hard to justify buying that one just because it has the connector on it already. Of there's a clear reason not to use a universal sensor, then I will stay away, but call me crazy, I have other priorities. There's over 150k miles on my car and things are starting to go. I'm really just trying to narrow down what is causing the issue I am experiencing, and if the sensor appears to be the cause, I will reinvest in a better part in that case.

Your choice. Your money. You get what you pay for.

I bought a Denso application specific upstream sensor - even though some on this board had not had good luck with it - it's been fine for over a month now ... the original that I pulled out (defective heater(?)) was also a Denso ... at least ... I *think* it was original :-)