12v is your heater power. The .45 volts is just the ECU driver voltage, can't tell much from that. One of those other wires should be a ground. So four wires, one 12v, one ground, two go to ECU 02 driver.

You said you swapped the 02's, you mean left to right? So the fault did not follow the 02? if that is correct, the sensor is not your problem.

Disconnect the connector at the ECU - check the four sensor wires to ground using the ohm meter with the sensor disconnected, none should get any reading.

 

"on top of that downstream sensors almost never go bad"

Mine did, twice. Replaced all four of them recently with NTK units and for the first time since I've own it, the codes have gone away completely.

 

At this point I think I have rules out the o2 sensors. The B2S2 sensor still parks itself at .44 - .45 v after swapping left to right. The other three fluctuate.This under all driving conditions. When weather permits, likely next weekend I will try the ohm test for the harness. Beyond that I might read up on fuel curves and build a smoke machine to test the intake, etc for vacuum leaks, see if that sheds any light on things. Truck runs pretty well otherwise. Fuel consumption is low (10.5 mpg last tank) and idle is a bit rough. Thanks for the tips. Stay tuned for the next phase

 

If the upstream cycles and downstream does not you either have a wiring issue or an ECU issue. Although not super easy, you can test the ECU from virtually free by buying a used ECU/BCU/IC combo off of ebay, swap it in, and see if it goes away. Yes? You have found your problem? No? Sell it back on ebay for what you paid. You are out shipping cost. Wiring - check everything to ground.

 

Ok, I have it all mapped out to test the harness from o2 to ECU, just need time and weather. Should I disconnect the battery before unplugging the connector to the ECU or not necessary? Tempted to buy a cluster/BCU/ECU as back up. Good idea. Curious if anyone has had luck with ECU guys that repair/ refurbish your own as plug n play? I see several in the US and more in the UK. Thanks for the tips!

 

Not necessary to disconnect battery but never hurts.

 

Thanks for the help with this. I have this on hold until weather improves. I will let you know what I find out then. I am investigating a heater / defrost issue on another post since I had the glove box off.

 

Well weather broke just in time for MY OIL PUMP TO ACT UP!!
Back to the O2 issue. I got a chance to do a continuity test on the harness from the ECU (disconnected) down to the disconnected o2 sensor. I got correct results on PIN 1, 2 & 3. Number 4 goes to the fuse box and fuse #2 is good. So the wiring looks good. Not sure if this would have identified a short or not but the light lit up on all 3 and all three were correctly wired to the correct ECU pin. I also swapped the rear O2's left to right again to be sure. Cleaned the connecters and fired it up. MOVEMENT on right rear and movement on left rear! Why? Cleaning? Actually I am not out of the woods. Light came on and right rear acts lazy still. This has me leaning to rehabilitate grounds next. ECU, chassis, engine,etc. I did a intake smoke test to rule out upstream issues and all was tight except a slight wisp of smoke from the throttle shaft on the throttle body. Oil pump this weekend and grounds. TBD.

A thing on dielectric grease. Only adding because I have read peeps refer to it as conductive. It is not conductive and you really don't want to get it between contact surfaces. Only for keeping things dry from the exterior of the contact.

Also read on some o2 sensors they are engineered to draw air in from the wiring where it goes into the connector. very slight gap or something. Slathering all with grease or covered in dirt might not be good here. I will find out more on this.