I'm Looking at the o2 sensor data for my 2013 Corolla and don't know if B1S2 is bad or not. I've heard that o2 sensors in general should oscillate between 0 and 1 V but I've also heard that for newer Toyota vehicles, the o2 sensor should be steady at around .8V. I've linked an imgur post with pictures of my live data. I know that the A/F sensor in B1S1 is fine but I'm not sure what is considered normal for o2 sensors in Toyota vehicles.

At first the data drops really low for some reason and kind of stays there but it eventually goes back up and levels off after a few minutes. I was at idle during this time and didn't touch the throttle at all. Then I decided to see what would happen if I quickly revved it to 3500 rpm. I thought that would spike the data up and indicate that the car was running rich since I just revved it but the voltage went way down to .035V. Then it kinda moved around a bit and leveled off at .855V. The car isn't giving any codes so I would assume everything is fine but I thought this data looked a little weird.

imgur live O2 B1S2 data pictures

  • Sensor voltage varies between 0 and 1 v, this is normal for stoichiometric fuel control.
    – Moab
    Jun 9, 2020 at 19:17

1 Answer 1


Ok I think I figured it out. I was just thinking that the downstream o2 sensor, which is the one that I was looking at, was used to measure air fuel ratios when really it is only used to measure the efficiency of the catalytic converter. That is why it is not oscillating between 0 and 1 V. From what I’ve researched, downstream o2 sensors can still vary between 0 and 1 volts but will not oscillate rapidly. Instead the changes in voltage will be pretty smooth.

So in my case, there is nothing to worry about and the downstream sensor is working correctly. I’m linking 3 really short videos which helped me figure this out.

Just writing this in case anyone finds this post later and has similar concerns.




  • In case you curious the B1S2 you posted originally means bank 1 sensor 2. In an inline 4 engine there is only 1 bank - or a set or cylinders essentially - and sensor 2 means the second sensor for that specific bank - or downstream as you've discovered. In a v6 or v8 there are 2 banks of cylinder and double the sensors. As you can probably imagine you'd have B1S1, B1S2, B2S1, and B2S2...in most cases. Anyways, nice job on figuring it out yourself!
    – Techlord
    Nov 7, 2020 at 21:31

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