2009 Rogue - P0420 Code

[Dedpul]

So i switched back to the new O2 sensor again, now I'm almost confident that the voltage is dropping as soon as my foot comes off the accelerator pedal. When stopped, it seems to do what it wants. But when i have my foot down on the pedal, voltage goes up and sits around 0.9V (which is still too high, correct?), but voltage drops down to around 0.06v as soon as my foot comes off. I'll recheck the connections/pins but i am stumped.

[Dedpul]

Once fully heated, the O2 sensor doesnt really seem to drop down on the voltage until my foot is off the accelerator in which case it drops down to basically nothing. Also, at stop lights/signs, it seems to be fluctuating up and down 0.05-0.9V

[VStar650CL]

The signal will often drop out the bottom when you let off the gas. The ECM is really only looking at it when you're cruising, so patterns when you're driving stop-and-go can be anything. Your foot will affect the pattern more than anything else.

The above is what a healthy cruise should look like. It's from a Honda and the voltage levels are different, but a healthy waveform should resemble it. Note that the humps aren't generated by the sensor, the ECM starts riching and leaning the mixture deliberately whenever the driving conditions are right for evaluating the cat and the sensor. If the sensor response lags in time, the ECM calls that a bad sensor. If it follows in time but the voltage is wrong, it calls that a bad cat. Those shots you took while cruising shouldn't be jagged like they are, and the inconsistent pattern is probably confusing the ECM so it can't rich-lean properly. It might help to put up RPM and TP on the same graph with the O2 so we can pick out the spots where the O2 should be in monitor mode. Or maybe just put the car in cruise on a level highway. Taking a quick look at the A/F versus the HO2S might also help.

[Dedpul]

I've been trying to get readings from my A/F sensor as well but the readings from it seem off as well (i didn't get pictures this time unfortunately). From my understanding, A/F should also have a smooth up and down in voltage similar to the how the O2 readings should look. But my A/F readings stay pretty consistent (around 2.2v and then drop down to around 1v and sit there for a while) which just seems wonky to me. Would i be throwing another code if the A/F readings to the ECM were incorrect or would that also throw a P0420?

[VStar650CL]

When you're driving 2.2V is just about right for the A/F. It uses a completely different chemistry than the HO2S and responds much faster. Basically 2V is the dividing line, higher is lean and lower is rich. The ECM uses it directly for mixture control, not indirectly to analyze the cat like it uses the HO2S. We techs have a saying that the front sensor is for the ECM, the rear is for the government.

It's not unusual for the A/F to spike way rich when you accelerate, then bounce lean when you drop throttle. However, it shouldn't be staying very rich or lean for very long. So it depends what you mean by "a while". The ECM would be throwing a different code for a bad A/F, but when an A/F isn't flatlined high or low, it can be hard for the ECM to determine that it's working but lying. For that reason, yes, a bad A/F can cause a false P0420 among other things.

[Dedpul]

A/F at idle goes from 2.1 to 2.3V. At cruise (around 65mph) it stays around there (2.1-2.3V) but jumps up to between 4V and as high as 4.6V, never really saw it go below 1.6V. I obviously don't know what that means haha but it doesn't look good in my eyes.
B1S1 and B1S2 don't seem to have any correspondance. Mind you my reader can only do one chart at a time so the charts comparing S1 and S2 aren't perfect for comparison.

Do you think i have more than one issue? The cars runs relatively smoothly so I can't imagine there's something terribly wrong with it.
I'm convinced my actual smog is good, just something about the data the ECM is getting.

[VStar650CL]

There won't be any correspondence that's noticeable, and the A/F will almost always bounce around rich-lean when you're on and off the gas pedal. So it's hard to tell anything about it without also seeing either throttle position or engine speed on a parallel graph. Your steady-state voltages are healthy, so try getting a plot where you go from cruise to punched-suddenly and then dropped-suddenly. You should see a big rich spike (low voltage) when you punch the gas and then a big lean spike (high voltage) when you drop it, then it should steady out again. If it does that, the A/F is healthy.

[Dedpul]

Sorry, been dormant for a few days haha. Finally got to take a long trip for work and figured it was a good time to check some of the sensors. Also found out i can stack 2 graphs on top of one another with my scanner. So below are my findings, all were cruising at 60mph with very slight hills:

Picture 1- MAF/O2 Sensor comparison
The humps are from me making sure the MAF is working properly

Picture 2- O2 Sensor(downstream)/AFR Sensor(upstream) comparison

Picture 3- (same as 2, different time)

So it looks like everything is working together the way it should, but for some reason the O2 sensor drops in voltage. Does this tell you anything?

[VStar650CL]

The ripples in the A/F are the ECM riching and leaning the mixture to test the cat, those are entirely normal. Any time those aren't happening, the ECM is ignoring the HO2S and whatever data comes out of it isn't relevant. Looking back, I don't think I explained the HO2S very well. What you're looking for isn't the absolute bottom of the signal, you're looking for the centerline of the cross-count. In the graph, yours seems to be swinging between about 0.8 and 0.2. That's a 0.5V centerline, which is above the 0.45 threshold but just barely. Cruising with the cat lit, it should be more like 0.7V and the cross-counts should be less pronounced. Since that final graph did come from a cat-lit cruise, it means the sensors are working and you have either a weak cat or an exhaust leak that's letting in oxygen. What I'm puzzled about now is why the spacer didn't work for you.

[Dedpul]

I'll be putting in the spacer again today and running some more diagnostics. The video that was posted only showed one spacer being thrown onto the cat, but one of my close friends said to use 2. 1 drilled out, 1 not drilled out (to restrict air flow). Is there a "correct" method to it?

[VStar650CL]

No, you may need to fiddle with the spacers and try some things. The idea is to find a combination that deprives the sensor of just enough oxygen to shut it up. There are right-angle spacers too, which can sometimes be more effective because they make the exhaust pulses travel around two corners instead of one.

[Dedpul]

Good thing I grabbed 4 spacers! Lol
The first time I put one in, i simply drilled it out to 1/2" and screwed in the O2 sensor, so it really didn't change the airflow much i don't think. I'll keep trying different combinations and checking with the scanner

[Dedpul]

Seems to me that the spacer is actually making the readings slightly worse. I wasn't able to get a good consistent drive like yesterday, but a few things stood out to me (I marked them in red on the photo this time).
Seems to me that the low spike on the O2 sensor shouldn't be there. Also that 0.00 voltage was when I let off the throttle, but should it read absolute zero? Is this because of what you mentioned earlier, about the ECM ignoring the O2 sensor when A/F is changing? Sorry if I completely misunderstood.

FYI, I used LAMBDAB1S1 because the graph seemed better to me and when comparing to O2B1S1 they were the same graph.

[Dedpul]

Another thing i Just remembered, when i bought a new A/F sensor, the plug on it wasn't exactly the same, i had to cut down one of the guides on the side as it seemed to be in the wrong spot. The sensor looked like the same size and all the cables were on the same positions as the previous sensor. Only difference was the one guide on the side of the connector. Could it be a wrong O2 sensor somehow causing these readings? It doesn't seem like it to me since the A/F readings seem to be a steady up and down when cruising

[VStar650CL]

That's called a polarizer. It's intended to prevent exactly what you did. Yes, that could definitely mean a wrong sensor, and yes, that could definitely cause issues.

[Dedpul]

Ok, the sensor i have in there is PN: 234-9071 but the part that fits correctly is 234-9073 or 9074 (don't remember) but it looked like the only difference was the plug. Could this be causing those weird O2 sensor readings? I'm still piecing this all together, but finally getting somewhere i hope.

I have an ECM, proper AF Sensor, and a little piece of tech (last resort), all coming sometime in the next couple days so hopefully something fixes it. My smog is due in about 10 days

[casperfun]

Thank god we don't have emissions testing in my city, the annual car inspection is a pain in the a$$ already.

[Dedpul]

Fortunately i don't have the car inspection. Annual smog only. If i was a county over i wouldnt have to worry about emissions.

[VStar650CL]

The A/F is working great and the ECM is seeing the data, that O2 sensor is the issue. Those p/n's aren't even Nissan numbers, I have no idea where you got them. If you're going to search online, you should plug your VIN into NissanPartsDeal, find the Nissan p/n for the sensor, then use that to search for equivalents. Buying "lookalike" parts, especially stuff like sensors, is just about guaranteed to screw something up (as you seem to be experiencing firsthand). RockAuto has an excellent part-number lookup, it's tabbed at the top of the home screen. Plugging in the Nissan p/n will get you to the right aftermarket parts.