so I hooked up Techstream to my '05 with 66k miles the other day and ran a healthcheck. Everything passed except the O2 Sensors, B1S2 and B2S2 with the following numbers:

.45v MOR B1S2 15.5, min should be 20
Area3&4 B1S2 23.85, min should be 25
RSR *** B1S2 38.6, max should be 9.8

Area 4 B2S2 19.4, min should be 19.99
.45v MOR B2S2 15.5, min should be 20
RSR *** B2S2 17.2, max should be 9.8

I ran the car for a good 25 minutes, tested again, and the readings improved for the most part, such that 3 areas passed, 2 remained as fails, and 1 got worse.
.45V MOR B1S2 17.9
Area3&4 B1S2 20.04

Area 4 B2S2 19.4

I have no drivability issues or problems at all, and NO DTC codes. But its bugging me big time that I have a failure.
What is going on here? What are these downstream sensors really doing? Will I fail emissions test?

 

Post cat or bank 2 are for emissions only. Sniffers to see if you have cats. You should have no problem with emissions. I would not worry about it. Until you actually get a cel light it's not worth being concerned. Not sure in Maryland but in GA they don't even do a tailpipe test except 96 and under I believe. They just plug into the OD2 port.

I would also mention that one the arguments for running premium fuel has to do with preservation of the cats. This was something a Lexus tech told me when I had to replace the cats on my LS400. Most likely the previous owners were not running premium but 87 its whole life before I got it and that over long periods of time this will damage the cats. 87 octane retards the timing, less efficient burn, more unburnt fuel pushed out down the exhaust = carbon.

 

thanks...yes, in Maryland they hook up to your OBD2 port, read it, extort their $14 and you're on your way, every two years.

Good to know I have nothing to worry about.
I had heard that about premium fuel and cats. Thankfully, it looks like my cats have near perfect efficiency across about a dozen areas in the Techstream.
I'm going to spend some time with the Repair Manual, see if I can find out more about O2 sensor data. Amazing what it is in the factory repair manual, if you can get past the quirky English translations.

 

so i spent some time with manual 1 of the Factory Repair Manual, trying to understand what the monitor data is saying about these O2 sensors. Pretty interesting. Net is that the data shows a "fail" until a precise test sequence is accomplished, in some cases, 13 times in a row of starting, driving, idling, driving, idling etc, at specific speeds and durations. The ECM stores the cumulative data, for example, how long the O2 sensor stays in a > .45v position, signifying a rich or lean condition. Or how long the O2 sensor takes as it switches back and forth between rich and lean conditions. To set a DTC code the threshold is even higher than the "fail" the monitor is indicating on these tests. I don't have any DTC codes, which hopefully the emissions people will agree is good enough to pass. And more importantly, this level of "fail" indicates more a fail in not following the test sequence precisely, rather than a fail of an O2 sensor.

at least that's the way i understand it....if anybody knows differently by all means jump in.