o2 sensors replaced, CEL is back

[xmaciek82x]

Hey everyone, I had two CEL, one for o2 Sensor Circuit High Voltage (bank 1 sensor 2) and another one for o2 Sensor Circuit High Voltage (bank 1 sensor 1).

So those pretty much mean that both upstream sensors are going bad. I replaced both sensor with new bosch ones and bank 1 sensor 1 came back on while the driver side o2 sensor code never came back.

I data logged the voltage on all 4 sensors (upper and lower stream). Upstream sensor 1 (passenger side) voltage constantly moves between .01v to .8v when parked, and between 0v to 1.3v when driving. Downstream sensor 1 moves around those same ranges. But upstream and downstream sensors 2 (driver side) stay at a constant .3v unless I start driving.

I'm slightly confused now why the above scenerio is happening. Does the constant voltage cycling in the passenger side upstream sensor indicated its bad? Why would downstream sensor be acting the same way but not throwing any CEL? What are the odds that a new sensor would be faulty? Is there something else that can be wrong? Plugs were replaced few month back and nothing looked odd on them.

Any help would be great.

[xmaciek82x]

OK, for some unknown reason, I cannot edit my original post, so i guess I'll make a reply to myself with some further findings and corrections to my original post. Correction, above should read that original CEL was with bank 1 sensor 1 and bank 2 sensor 1. I also wanted to correct that after driving around and data logging, I noticed all 4 o2 sensors behaving correctly. Voltage moves between .01v and 1v.

What was odd is that bank 1 Short Term Fuel Bank and Fuel Trim bank 1 sensor 1 (not sure the difference between the two) both read 0%, while bank 2 moves accordingly with +/- % readings. Would this indicate fuel problems? If so, what could be the next thing to troubleshoot/replace?

[PathyPop]

It sounds like maybe the sensors aren't bad but they are doing their job? Very unlikely they would code at the same time if bad. Were you doing any work before the code, like cleaning the intake, using a fuel additive, had a vacuum or injector leak, even changing the air filter. I used carb cleaner once to clean the intake and got codes on both banks but they cleared after a few miles once the stuff burned off. Now I'm sure to only use injector cleaner.

I'm no expert but I see many issues of the O2 triggering with the assumption it is a bad sensor when it was really something else, at the worst a bad cat.