2008 Tacoma- p0136, but everything looks fine?

Working on my pastor’s 2008 Tacoma 2.7L with 77,000 miles, and getting a bit stumped. He just bought this truck, and on the way home the check engine light came on. Had the code read, and it was:
P0138- O2 Sensor Circuit High Voltage (Bank 1, Sensor 2).
He replaced the O2 sensor, the EFI relay, had the code cleared, and a less than 100 miles later the check engine light came back on- this time:
P0136- Oxygen Sensor Circuit Malfunction (Bank 1, Sensor 2.) This code is currently active, and also pending.

This is when he called me, and I am a bit stumped- because as best as I can tell from my scanner, the o2 sensor is operating as it should. (this Toyota has an upstream Air/Fuel Ratio Sensor, and a downstream Oxygen Sensor)

the “book” says at steady, warmed up idle
-upstream sensor should read at 3.3volts. I show 3.4volts
-downstream sensor should read between 100 mV and 1000mV. I show about 800-900mV, with it decreasing as expected immediately after releasing the throttle and idle drops. After I goose the throttle and let off quick, it does drop below 100mV, but only for a second or two- then it climbs back up to 800-900mV.
-downstream sensor should read above 5 ohms. I show over 5ohms constantly (usually somewhere around 200ohms)
-Fuel trims are good: usually about 5 numbers apart (ST reading about 0 to -2, LT reading around 3 or 4.)

I did a smoke test on the intake, and found no leaks. I have done a visual on the exhaust, and didn’t see anything that looks like it’s a leak. Even thought the p0136 is active, there is no freeze frame data to be found, so I can’t see if I have an intermittent drop out of some of the readings.

I don’t deal much with gasoline emissions issues, and deal even less with Toyota’s (although my son did just buy one, lol, so it is in my future,) so any guidance/input/direction would be appreciated.

That code P0136 code indicates it might be a bad harness or connector. Depending on the frame update rate of your scanner, you might not be seeing a drop-out or intermittent signal from the sensor. Maybe check the connector for corrosion and the wiring harness for damage as a first step.

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I checked the connector (component and harness sides,) and didn’t see anything. All looked clean and shiny. I will reverify.

That center point is too high, indicating that the fuel system is rich.

Both P0136 and P0138 can be caused by a failing air/fuel sensor. Are the fuel trims out of the normal range?

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it is on the high side, but from what I am reading, still within specs, is it not?
Fuel trims seem good: usually about 5 numbers apart (ST reading about 0 to -2, LT reading around 3 or 4.)

Here are some snapshots I took last night after my drive home. Does this help any?
1 2 3 4

I think you got it. I went ahead and replaced the AFR, and the code has not returned- even in a long drive on Test Mode.

here is after numbers- o2 voltage came way down at idle.