O2 sensors B2S1 & B2S2

2006 Tundra, event sequence:
Overfilled oil by just a bit.
~30 days later I get codes indicating downstream O2 sensors have a problem
Replaced downstream O2 sensors with Walker brand sensors which measured 9V when engine was cold & then 4V after warming up.
Returned Walker sensors & got Denso sensors. Voltage measured 0.7V
Check engine light came on ~15 minutes after installation of new Denso sensors.
Replaced both catalytic converters & used existing Denso sensors.
Check engine light came on ~45 minutes into a trip after cats replaced.
I now (7/6/21) have a P0136 (B1S2 O2 sensor circuit malfunction) code and a P0158 (B2S2 O2 sensor circuit high voltage) code.
The OBD adapter graph of both the B1S2 and B2S2 sensors shows the voltage at 0.7V going to 0.1V after revving the engine and letting up on the accelerator. Voltage then returns to 0.7V at idle.

Any ideas?

 

Did you replace the front sensors as well?

 

No codes have indicated front sensors are faulty.

 

Did you replace the cats or did a shop do this? I would double check for any exhaust leaks - I had an old pathfinder that used to throw these codes when the flange gasket behind the cats went or the muffler had a hole.

As these are just cat efficiency codes, you can install a simple circuit to tie in the sensor wire to permanently resolve them.

 

Tires Plus replaced the cats with new, not refurbished ones.

Do you have a link to info about the circuit you referred to?

 

Replace the front sensors. Not the first time someone has had the same codes show back up after replacing the rears without ever throwing codes for the front.

 

how much is just a bit? Cause im running a full 7 qts.

 

My 2wd takes 6 qts IIRC.

 

6.6? And the 4.7 has enough room for an extra .4

 

Like 6.0 almost exactly. Different pan than the 4x4.

 

This site ( https://mkiv.com/techarticles/oxygen_sensor_simulator/index.html ) has a circuit similar to what I used. If you look on the TI spec sheet ( https://www.ti.com/lit/ds/symlink/lm555.pdf?ts=1625609356079&ref_url=https%3A%2F%2Fwww.bing.com%2F ) - it details how set up the oscillator and tune the voltage divider.

Good thing about old vehicles is that they are narrow band, so this circuit will work. Bad thing is that wide band allows more flexibility, including air flow changes without having to install a custom tune.

 

Black electrical tape would take care of that engine light.

 

Yes - and easier. Unfortunately part of emissions in my area is OBD check. I used to drive around with the light on and didn't care until I missed a misfire code that would have predicted a coil failure.

If I had the option, I still would have taken the tape route.