Upstream O2 VERY HIGH (2.5 volts)

I have a 2013 Nissan Sentra SR, 1.8, CVT. I’m hoping some of you can help me sort this puzzle out.

Background Facts:
The vehicle starts shaking when I put it in reverse or if I turn on the AC unit.

Assuming that the shaking was caused by the mounts, I replaced the engine and trans mounts, to include the bottom rear mount that looks like a dog chew toy. Replacing the mounts helped the shaking a “little bit” but the shaking is definitely still there and very noticeable.

No obd codes. Checked the live data and it idles at approximately 700rpm while normal operating temp. I then turn on the AC and the rpms go up to approximately 800 and then immediately drop back down to 700 rpms. The car shakes in reverse and in drive and when the AC is turned on. The shake goes away when I press on the gas or rpms go up.

Fuel trims appear normal on the road. Both LTFT and STFT add up to less than 5.

For the past week or possibly longer, the upstream O2 sensor fluctuates up and down between 2.7 and 2.1 volts. And even saw it read as high as 3.6 volts. The downstream O2 ranges between 0.4 and 0.7 volts.

There is also an obvious smell of unburned exhaust.

No codes yet but with the upstream O2 sensor reading that high for at least over a week, I’m assuming that it’s only a matter of time before a code shows up.

Any thoughts on this?



The video implies that the problem is automatically the CAT if the O2 sensors aren’t graphing the way they should. Could be fuel regulator, O2 sensor, etc. Right? Im hesitant in jumping into changing a $700 without ruling everything else out.

Two different types of sensors; the upstream is a wide band air/fuel sensor, the downstream is an oxygen sensor, they have different voltage operation ranges.

That should be an indication that the fuel delivery system and exhaust sensors are operating as designed.

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Look at Lambda instead if that value is available on your obd reader. Lambda of 1.0 is what you are looking for. Lean is greater than 1, rich is less than 1. If your reader shows A/F ratio, it should operated around 14.0. Lower is rich, higher is lean.

Seems that stft and ltft are in the safe range. Take lambda or A/F readings and post them.

Also sounds like the throttle body may be dirty or failing

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I have seen something like this twice.

One time is was bad grounds on the sensors/ECM. They were just dirty and cleaning them worked wonders.

On another car it was simply a bad battery. IT was starting the car but barely. I didn’t realize how bad this was until I replaced it and the car ran a ton better. These sensors rely on a certain voltage. You may be within spec enough not to throw a code but still not right on the money.

I don’t see anything obviously wrong w/measurements. Do you notice a gasoline odor from the exhaust all the time, or only when first starting engine? I’m guessing problem causing the engine to shake under those conditions is in the ignition system. Could replace spark plugs, plug wires (if so configured), and engine air filter, has to be done as part of a tune-up anyway, and might help. Measuring engine compression numbers probably worthwhile too, esp if engine has ever seriously overheated or run w/low oil.