P0031 Code, but reading voltage at sensor

The short version is that my truck is throwing the P0031 code (O2 Heater circuit low voltage B1S1) but I can observe battery voltage on both heater wires, when truck is keyed on and when engine is running.

The Long version is this: A while ago my truck started throwing the catalyst inefficiency codes for both sides, I tried Cat Clean and then 4 new O2 sensors but no joy, codes still present. Found an exhaust leak at one of the y pipe joints, replaced all three gaskets, still didn't solve the problem. I live in California so that sucks, because at that point it meant I probably needed new cats, which would have to be factory. No way I'm paying for those. So I ordered the URD O2 emulators, installed and right away the Cat Inefficiency codes went away... and were replaced with the B1S1 low heater voltage code. F*ck me.

Now the URD emulators connect in line with the rear sensors, so I can't think of any reason they'd be jacking with the upstream sensor heater voltages. So I set out with my Fluke meter to do some testing. Thank God it's Bank 1, because the Bank 2 upstream sensor is a bitch to get to.

Here are the Voltage measurements I found when I checked (truck running):
O2 Heater Fuse (both sides) - 13.4 V
Voltage in at O2 connector - 13.4 V
Voltage out at O2 Connector - 13.3 V

I've tried clearing the code multiple times, both when the truck is just keyed on and when it's running. The code will clear for a few seconds and then comes right back.

So the question is; does anyone in another state, without smog requirements, want to buy my truck?
JK, I love my truck, please help.

 

I believe that even though the Code is labeled the O2 Sensor.
It actually pertains to the A/F sensor.
You can check below for the locations.

http://www.cardiagnostics.be/-now/i...k_2A-F_and_O2_Identification_T-SB-0398-09.pdf

 

The fact that document differentiates between "O2 sensors" and "A/F sensors" is very weird to me, since those two terms have always been the same thing in my mind. Maybe they're different in that doc due to the wide-band/narrow-band distinction, idk. But either way, my code is for the B1S1 sensor, passenger side and pre-cat, that's the one I was checking, by whatever name it wants to be called.

 

From the service manual:

HINT:
• Although the DTC titles say the oxygen sensor, these DTCs relate to the Air-Fuel Ratio (A/F) sensor.
• Sensor 1 refers to the sensor mounted in front of the Three-Way Catalytic Converter (TWC) and located near the engine assembly.

If you look at the description of what triggers the code you will see it is a current reading or lack of that triggers the code. You can have voltage present with ZERO Current Flow.

In other words you have an open in the circuit somewhere Wire, heater or heater relay or the ECM is defective.

The ECM sets DTC P0032 or P0052 when the current in the A/F sensor heater is more than 10 A.
Conversely, when the heater current is less than 0.8 A, DTC P0031 or P0051 is set.


From the service manual:

DTC No.
P0031 and P0051

DTC Detection Conditions
Air-Fuel Ratio (A/F) sensor heater current less than 0.8 A (1 trip detection logic)

ConditionsTrouble Areas
•Open in A/F sensor heater circuit
•A/F sensor heater
•A/F sensor heater relay
•ECM