1998 4Runner 2.7 P0136- What should the post cat O2 sensor waveform look like?

Question

I have a P0136 on my 1998 4Runner 2.7 3RZ-FE. It uses both narrow band sensors (pre cat and post cat) Looking at the waveform of the post cat sensor, often upon acceleration it drops to 0 volts. Common sense suggests that the pre cat sensor waveform should fluctuate as the mixture is cycling from reach to lean and the post cat should remain steady (if cat is working) but should it drop to 0 volts? ST fuel trim is about 3% whilst LT is -10.9%, I’m wondering if I’m dealing with a faulty sensor..
I used the Toyota Techstream since it doesn’t have a very good recording function I had to physically film the data, here’s a video of a short drive at operating temperature: 
Blue trace is pre cat sensor
Green is post cat sensor
Red is RPM
Yellow is vehicle speed

https://youtu.be/icQMDPcE02Y

I’ll appreciate any input.

Old_Fossil · Answer

P0136 indicates that the exhaust is running too lean. When the voltage on a 02 sensor is high it is running rich, low voltage is running lean.

Most of the time P0136 indicates a defective sensor or a leak in the air intake system.

If it is same thing that happened to me (the air leak one) check the rubber pipe between  the air filter assembly and the intake manifold. I had 2 2" cracks in the rubber which caused a drop in the volume of air entering the intake manifold. Mechanic had to seriously clean the throttle body and the MAF sensor element and then reprogram the ECM after replacing a new ribber pipe.

1998 4Runner 2.7 P0136- What should the post cat O2 sensor waveform look like?

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