Asked differently:
Key on, engine off, OBD reads N/A for both Up & Downstream O2 sensors on the right side (but a steady signal for Bank 1). Need I look any further than electrical / ECM?

 

Say again why you're sure it's not just dead sensors? Above you say that "the values are similar when compared to the two I just pulled out" but according to your tests, those values are zero.

 

From my experience a broken ground or disconnected upstream sensor should read about 400mv on an odb scanner

 

Sorry, yes, it is possible that all 8 of them are dead, it just seems unlikely. I swapped the right side sensors for the “known working”, previously on the left, sensors and I still get N/A on OBD for the right side. If it is the sensors, it would mean the two 3-month-old RH sensors are dead, the two new RH sensors are dead, and now I have somehow killed the 3-mo-old LH sensors.

Again, all 4 RF test good for continuity to the ECM. Starter fluid and water spray tests elicited no change in engine or OBD state, but I suppose there could still be a catastrophic leak somewhere. I am not confident I reached all of the head gasket.

Will a small leak lead to an N/A? Does N/A mean that the ECM is seeing no signal at all, or can it mean a zero reading? If I drove it too long with this fault and killed the cat, would that somehow lead to N/A on new sensors?

I’m down to taking it to the dealer or bucking up for the ECM swap.

 

A bad sensor, stuffed cat, or leak should not read N/A, there should always be a signal. The ECM puts out a 400mV signal on the positive side of the (upstream at least)O2. To verify the ECM is working unplug the upstream O2 and check voltage with the Neg side of the meter on the battery Neg.

How did you perform your continuity test?

 

Okay, thanks for clarifying. It does seem highly unlikely that all of them would be dead, so I would cautiously assume that you should be getting some reading out of whichever ones you have in there.

 

I've been struggling with a similar issue, bank 2 sensor 1, but I get the reading of around .45 that will very slightly down to maybe .3. I consistently get codes P0154 and P1174.
I've swapped the left hand and right hand front sensors and back, and the driver side works with either sensor, while the passenger side has the same reading with either, so I'm sure it's not the sensor. Next step is to check continuity all the way to ECU. I've written down which pins are which. What might cause a break in continuity short of an obvious chewed up wire from an animal?

 

I had a ground trace inside the ECU that failed. It was underneath the connector block so I just put a jumper wire to ground and was good to go. Disconnect the harness to the ECU and check continuity from the o2 ground pins on the ECU to a body ground.

 

Ok, Mollusc, thanks for sticking with me.
Sandman, I also get a very steady 459mv. To check for user error, I looked at the left also (464mv)..
The continuity test was from the harness connector at the sensor to the #2 plug at the ECU. All 4 leads conduct. On the ECM side, at your suggestion, I tested the appropriate pin (2-13, IIRC) to the ground with no issue.
For a moment I was hoping for damage at the connector, but no such luck.

 

JBullard,
Common wisdom is that the harness can wear or melt where it passes behind the engine. Continuity test with long alligator leads to the ECM connector. Sandman's post & pics on loose pins is very helpful. Top tip: #2 connector (2nd from left) is pretty well locked in place by 3 thru 5 - just pull 'em all. While you're testing for continuity, you may as well check for resistance. Give the connector a good wiggle test, too. You've pulled those connectors apart, right? I can easily imagine them getting tugged a little too hard.