2005 Toyota Tacoma 4.0 P0051 heater ckt.

 I have tested all four wires from the B2S1 (drivers front) sensor, too the PCM.  None are shorted,open.or shorted together.
Someone has replaced the 12 volt wire from the fuse box to the O2 sensor ,heater power. At the AFS B2S1. Its in good working order.
 History: This has had all the catalytic converters replaced. Both AFS are new and have been switched Left to right just for testing.
    Both rear O2 sensors are also new.
 The P0051 is a Hard fault.   You can see in the screen shot, B2 (green) duty cycle for the heater ckt, tries to turn on. It turns off quickly after that.
                      The B1 duty cycle continues on normal operation.  The Pcm was replaced, but I have the same results.
  What is the Pcm seeing to turn off the duty cycle On B2.? Giving the p0051.
 

Found loose/stretched pin in connector of O2 sensor.
Repaired connector , rechecked same connections at the pcm. Decided to look at voltage instead of duty cycle .
The pcm still goes too Fail-Safe mode. P0051.

The voltage behavior in your last capture is definitely atypical. Normally, when the PCM doesn't like the heater current, it disables the heater driver (12V on both heater wires). This one is going to 100% duty cycle (12V on heater power, 0V on heater control).

If you have a current probe, I'd be interested to see how much current that circuit is drawing. The PCM will shut the driver off in response to too little OR too much current.

You could also try installing a small incandescent bulb in place of the O2 heater for testing purposes. Clear the faults, start the engine and observe the bulb. Does it even try to light?

Thank you. my thought after I posted was ,link in a 168 bulb . it being a 5 watt bulb, if i remember correctly.
Also setting a low Amp on it. The threshold being 0.8A for setting The p0051.
The power wire that someone installed , the solder joint was rotted. The heat shrink was holding together enough to create voltage sometimes.

Installed  a  fog bulb in place of  the O2 sensor. then Grounded the heater control . Nice and Bright.
You can see Amp on the B1 working . Then B2 does nothing.     What is the PCM seeing to turn off the Heater Grounding Ckt?
 

Me Grounding the Ckt by hand , showing it has the potential to work.

Still broken..... Pcm still not grounding the heater CKT.
No thoughts, suggestions , ?