O2 S1/B1 low volts at pigtail

[work truck ram]

Bit of history because the last repair is often the source of the current problem. 04 Ram 1500 3.7 with 280K I am the OG owner. Head gasket had minor weep so figured she earned a complete tear down rebuild. Enginetech piston rings that came in the seal set refused to seat and pumped oil out the exhaust. Tear down again with new seals and rings, Problem solved. Runs great again.

The new problem. Bank1 sensor 1 low voltage and heater fail codes. Fair enough with oil and antifreeze bath so replaced them all. Still have the code. Swapped the sensors around and problem stayed on B1S1. Scan is showing 1.4V steady on that O2. Both downstream showing same .5V. Next tested the s1b1 plug with O2 unplugged key on engine off and at idle. On the 4 pins I get.
1) 0V OL to ground (signal?)
2) 0V continuity to ground (ground)
3) 4.15V (heater hot)
4) 2.5V (reference?)

Is the low voltage because my digital meter is confused by a possible pulse width modulation on the 5V? If so why is heater so low instead of bat volts? Pinched wire acting as a resistor? Sudden, random, PCM failure?

I have built wiring looms for several nonconventional engine swaps but on slightly older GM cars. Don't know what plugs are C1 and C2 on PCM. Guessing top and next down. Plug wire numbering order for wire 32 on each plug. Never worked with O2 having a reference signal. PCM looking for 5V plus the O2 generated V on signal?

 

[work truck ram]

kept reading to only use fill in name brand O2 sensors. brand isn't exactly the issue. certain brands clearly differentiate upstream and down stream. Most of the cheaper sources list them as interchangeable because they use the same plug. they are not the same part at all on these engines. I was sent 2 downstream "universal" bosh O2 sensors. Replaced them with walker upstream because they were in stock. Problem solved.