O2 Sensor voltage readings

[Bruce2293]

I had a code come up for my O2 sensor. I don't remember the exact code or what one of the 4 sensors it was for. Since then the code has gone away and after trying to read it again, my code reader hasn't come up with anything. I decided to watch the voltages while the truck is idling after letting it warm up.

My two upstream sensors are reading pretty alright. B1S1 - .1-.7V and B2S1 .1-.8V

My question is with the two downstream sensors. They are both reading steady voltages. I'm not sure if downstream is supposed to be alternating the same as upstream. My B1S2 is holding at .78v and B2S2 at .84V.

 

[LoneWolf3574]

Your downstream voltages should be holding steady and your upstream should vary, so what you're seeing is normal. The steady voltage is an indication that your catalytic converter(s) is (are) working properly, they don't necessarily need to be exactly the same.

Check your sensor wiring for damage, it could have shorted out temporarily and sent the code.

 

[Bruce2293]

Should the downstream sensors be reading closer to .45V though? I thought they are reading a little high.

 

[LoneWolf3574]

I won't claim to be any sort of expert on this, mine are usually a steady 0.7-0.8V and as far as I know, that is a good number. Somebody correct me if I am wrong here, but so long as the voltage is not staying low (below 0.5V I think) and it is staying relatively steady, your sensor and catalytic converter are operating normally.

As long as you are not seeing anything like the lowermost waveform, you are fine. You should see something like the middle over time after your cat(s).

 

[Fast69Mopar]

I had a code come up for my O2 sensor. I don't remember the exact code or what one of the 4 sensors it was for. Since then the code has gone away and after trying to read it again, my code reader hasn't come up with anything. I decided to watch the voltages while the truck is idling after letting it warm up.

My two upstream sensors are reading pretty alright. B1S1 - .1-.7V and B2S1 .1-.8V

My question is with the two downstream sensors. They are both reading steady voltages. I'm not sure if downstream is supposed to be alternating the same as upstream. My B1S2 is holding at .78v and B2S2 at .84V.

The upstream oxygen sensors switch from high to low, lean to rich, to maintain the commanded AFR, or Air Fuel Ratio. The downstream oxygen sensors are there to monitor the catalytic converters and for making Long Term Fuel Trim corrections.

In my "professional" experience, when the downstream sensors go above 0.80V and stay above that voltage the PCM will set a corresponding DTC for catalyst efficiency.

Your voltages are typical for a truck like the ones I see on a daily basis.