2009 Rogue - P0420 Code

[Dedpul]

Hello,
I'm brand new to this forum, in search of answers and hoping to bring some answers myself eventually. Let's get to it. Here's my situation:

Trying to get my '09 Rogue smogged but I have the CES light and P0420 code is my only engine related code. I have replaced in the past week:
-Spark Plugs
-Ignition Coils
-Catalytic Converter (and gaskets)
-Upstream & downstream AFR/Oxygen Sensor
-Cleaned Air Filter, MAF Sensor, Throttle Body
I replaced all of these separately in order to hone in what is causing the code. Yet the code is still popping up after only 40 miles of driving since reset. It's not misfiring as far as I can tell and am seeking other opinions at this point before going to a shop.

The car drives fine besides a little shaking due to engine mounts, and some transmission issues (who doesn't? )

[casperfun]

Give these a try. Hope something works just in case I need this fix.

[VStar650CL]

P0420's with aftermarket replacement cats are pretty common, because a lot of times the cheap ones are inefficient. The most reliable fix that will still give you some warning (although maybe not much) if the new cat fails is a sensor spacer. There are tons of them on eBay and Amazon, just search "O2 spacer".

[Dedpul]

P0420's with aftermarket replacement cats are pretty common, because a lot of times the cheap ones are inefficient. The most reliable fix that will still give you some warning (although maybe not much) if the new cat fails is a sensor spacer. There are tons of them on eBay and Amazon, just search "O2 spacer".

Well, I tried the spacer and it threw the P0420 code about 10 miles sooner than without it. Not sure if that means anything, but I did take it to my local Nissan dealer this morning and had them run a diagnostic on it. They wanted to put a new cat on it and claimed they couldn't do further diagnostic testing to tell me for sure what's wrong with it until I get an OEM cat on it. Voltage on the downstream O2 sensor was off (consistent spikes in voltage) from what I could tell in the graphs they briefly showed me. It seemed like they were very weird about it (Didn't want to run further diagnostics because I had an aftermarket cat, and they didn't want to print the graphs for me to take home and look at).

As soon as my car cooled off when I got home, I took out the new cat, and put my original back on, hoping they'll run REAL diagnostics on my car.

Note: my original cat was CLEAN and in good condition when I took it off. Meaning the little honeycomb filter at the end was clean and white, and even after soaking it in dish soap and water, the water was clean too.

[VStar650CL]

Do you maybe have a tiny exhaust leak somewhere between the front and rear cats? That can cause a spurious P0420. In particular, was a new crush ring used on the cat outlet, or maybe the sensor isn't sealing in the pipe? If there are no leaks or if the readings are actually spiking (as opposed to ramping), you may have a wire or pin-fit issue. High resistance in a wire or connector is a possibility, since electrically the sensor is a balance resistor.

[Dedpul]

Do you maybe have a tiny exhaust leak somewhere between the front and rear cats? That can cause a spurious P0420. In particular, was a new crush ring used on the cat outlet, or maybe the sensor isn't sealing in the pipe? If there are no leaks or if the readings are actually spiking (as opposed to ramping), you may have a wire or pin-fit issue. High resistance in a wire or connector is a possibility, since electrically the sensor is a balance resistor.

Nissan said no exhaust leaks found. Everything is sealed up. I did put a new crush ring and manifold gasket when installing the new cat, and again when putting the original back on earlier today.
I did have serious electrical issues after a trip to California a few months back. My positive battery terminal completely corroded over (seemed like overnight) and my alternator had gone bad a few days later. Was fighting electrical issues for nearly a week before I was able to drive the car normally. I'm wondering if I somehow shorted something or received a power surge of some kind. Should I possibly think about replacing the ECM itself? My car does shift a little funny from time to time too, especially after long drives on the highway without stopping. If I come off the highway and am stopped, I push on the gas to go and it starts to roll forward but no power gets delivered. Its not until I stomp on the gas that it lunges forward and starts moving again.

[VStar650CL]

Was there over-voltage when the alternator crapped? Nissan modules will generally stand about 15.5V without hurting anything, more like 16.0V if the engine isn't running. Above that it's a crapshoot. "Spiky" readings on an HO2S certainly aren't normal, so yes, maybe the ECM is running with crap-colored glasses and doesn't know it.

[Dedpul]

I couldn't tell you if there was over-voltage honestly. I just remember thinking my transmission was going out because the car would start, but it would not drive. First I replaced the battery terminal, then I replaced the battery the next day, which seemed to HELP, but not fix the problem. That's when I finally replaced the alternator and the car drove fine afterwards. I should also mention the P0420 code has been there since before that happened, but nothing was ever done about it (my sister owned the car at the time). The code was on and off for about 2 years, it used to go away after long drives on a hot day but eventually just started to stick (beginning of the year). So I guess part of the difficulty of my situation is that it may be more than one issue. In my opinion, the physical exhaust stuff should be good now (cat, sensors, etc) since they were replaced.

[VStar650CL]

Okay, leaving out the battery stuff, the only thing that's left is either resistance in the sensor wiring or an A/F sensor (front O2) that's working half-arse and fooling the ECM. Put your scanner on it at a freeway cruise with the car warm and the cat lit, the A/F sensor voltage reading should be rotating very slightly around a 2.2V level. The A/F reacts directly to mixture with no time integral like an O2, so if the voltage is off by much then maybe the problem is in the A/F and not the HO2S. If the A/F checks out, then you need to find out what the ECM is objecting to in the HO2S signal. With the cat lit, the HO2S voltage should oscillate around 0.6~ 0.8V volts at a steady cruise. The threshold is 0.45 volts, if the oscillations cross that line then a P0420 gets thrown. It's pretty straightforward, the ECM only uses voltage to evaluate the cat and only uses oscillation time to evaluate the sensor, so it would be throwing a different code if the swing rate was off. If your scanner will do it, you could also clear the code and then capture the freeze-frame info when the code reoccurs, so we can try to duplicate the conditions if necessary.

[Dedpul]

Okay, leaving out the battery stuff, the only thing that's left is either resistance in the sensor wiring or an A/F sensor (front O2) that's working half-arse and fooling the ECM. Put your scanner on it at a freeway cruise with the car warm and the cat lit, the A/F sensor voltage reading should be rotating very slightly around a 2.2V level. The A/F reacts directly to mixture with no time integral like an O2, so if the voltage is off by much then maybe the problem is in the A/F and not the HO2S. If the A/F checks out, then you need to find out what the ECM is objecting to in the HO2S signal. With the cat lit, the HO2S voltage should oscillate around 0.6~ 0.8V volts at a steady cruise. The threshold is 0.45 volts, if the oscillations cross that line then a P0420 gets thrown. It's pretty straightforward, the ECM only uses voltage to evaluate the cat and only uses oscillation time to evaluate the sensor, so it would be throwing a different code if the swing rate was off. If your scanner will do it, you could also clear the code and then capture the freeze-frame info when the code reoccurs, so we can try to duplicate the conditions if necessary.

Wow! Thanks for that great tip. I'll try it out tomorrow when the code comes back up. I've driven it less than a mile since i put the old cat back on so we'll see what happens. I really appreciate your input on this

[VStar650CL]

You're most welcome. Don't call me Agatha, but you might know by now that I love a good mystery.

[Dedpul]

Okay, leaving out the battery stuff, the only thing that's left is either resistance in the sensor wiring or an A/F sensor (front O2) that's working half-arse and fooling the ECM. Put your scanner on it at a freeway cruise with the car warm and the cat lit, the A/F sensor voltage reading should be rotating very slightly around a 2.2V level. The A/F reacts directly to mixture with no time integral like an O2, so if the voltage is off by much then maybe the problem is in the A/F and not the HO2S. If the A/F checks out, then you need to find out what the ECM is objecting to in the HO2S signal. With the cat lit, the HO2S voltage should oscillate around 0.6~ 0.8V volts at a steady cruise. The threshold is 0.45 volts, if the oscillations cross that line then a P0420 gets thrown. It's pretty straightforward, the ECM only uses voltage to evaluate the cat and only uses oscillation time to evaluate the sensor, so it would be throwing a different code if the swing rate was off. If your scanner will do it, you could also clear the code and then capture the freeze-frame info when the code reoccurs, so we can try to duplicate the conditions if necessary.

So i got a better scanner this morning and all my sensors seem to be reading fine besides Bank 1 Sensor 2 (Oxygen Sensor. Voltage holds at about 0.8V for 2 secs, dips to nearly nothing (0.05V) for a second, then goes back up to 0.8v for 2 secs. Graph is just up and down on the voltage

[Dedpul]

Edit: I forgot to mention all this was done at idle

[VStar650CL]

They don't really spec them at idle because the ECM pretty much disregards them, but that sure looks like a bum sensor. It's going both too high and too low. You can double check it at cruising speed with the cat lit, but if it's doing the same thing then your new sensor is a bummer.

[Dedpul]

I managed to get 2 pictures while driving. My concern is that this sensor is brand new, i still have the original so i guess i could put that one in and see if it's still reading the same.

[VStar650CL]

If the old one does the same thing then it's wiring, probably a resistive connection.

[Dedpul]

Haha, old one did the exact same thing. Gotta love the electrical stuff

[VStar650CL]

Check the pin-fits before you go nuts looking for broken wires. The fact that it looks normal at idle but breaks up on the road is what you'd expect from a broken or bouncy connector spring.

[VStar650CL]

PS - A safety pin with 0.024~0.025" diameter is perfect for the ECM pins and probably right for the sensor pins. If you do find a bad one, I can get you either kind and help with disassembly and replacement. The pin should drag slightly when inserted, if there's no resistance then the spring is messed up.

[Dedpul]

Would you happen to know which connector on the ECM it would be on? And also I'm assuming the wires go straight from the O2 Sensor connector into the ECM? No other connectors in the middle?

I tried to look at a wiring diagram but i could not find the exact pin it belongs to. This is the site i found the diagram on:
http://www.nirogue.com/wiring_diagram-387.html

[Dedpul]

To me, looks like it's connector F51 Pin 2 but that's saying it's "Throttle Control Motor Power Supply"

[VStar650CL]

There shouldn't be any intervening connectors, the A/F and HO2S are always wired straight to the ECM. I'll find the callout for the ECM connector and post back.

[VStar650CL]

Okay, use this link into the ESM, all the stuff you need is on pages EC-1250 and -1251:

https://www.nicoclub.com/service-manual ... 9%2FEC.pdf

The HO2S is connector F31, it has 4 wires but you're only interested in two. The blue wire on pin 1 is the HO2S signal (data), the pink wire on pin 4 is sensor ground. The 12V supply is only for the heater and that would be throwing a different code, so the other 2 wires are irrelevant. When looking at the connector drawings, they're all shown from the harness side (where the wires enter), so you need to mirror them when checking pin-fits on the terminal side. One word of caution when using a safety pin as a spread-terminal gauge, get out your caliper and measure it. Under no circumstances use a pin thicker than 0.028", you can spread the spring and permanently damage it. The ECM connector is F8, which is the largest of the three ECM connectors. Notice that pins 73~80 are larger than the rest, you can use that to orient the connector correctly for checking. Pin 33 is the blue signal wire, pin 35 is the ground wire. From the way the circuit is behaving, I suspect the problem is in the ground connection. If you don't find any pin-fit issues, try sticking a safety pin or T-pin into the back of the sensor connector on the sensor side, then jumper it temporarily to a chassis ground. If the sensor starts to behave itself, it's perfectly acceptable to make the jumper permanent, just scotchlok an auxiliary ground onto the sensor wire. Don't try to splice it, butt crimps are a bad idea underneath the car and the wires on the sensor side are steel and won't take solder. Scotchlok it and then seal the scotchlok with RTV. If the problem is in the signal wire, I suggest removing the backshell from the ECM connector and run a new parallel wire all the way from the ECM to the car side of the sensor connector. That run will be copper, so solder-shrinks will be the right splice type. Look up this thread for how to get the backshell off the ECM connector:

post6828764.html

[Dedpul]

You are a godsend. So helpful, thank you. I don't know why Nissan didn't look at the O2 sensor readings when I went in for a diagnostic but i suspect it's because they assumed the aftermarket cat was the cause of the issue. I'll try to check those pins tomorrow if I have the time. If I take off the backshell for the connector does that give me access to those springs as well?

[VStar650CL]

You are a godsend. So helpful, thank you. I don't know why Nissan didn't look at the O2 sensor readings when I went in for a diagnostic but i suspect it's because they assumed the aftermarket cat was the cause of the issue. I'll try to check those pins tomorrow if I have the time. If I take off the backshell for the connector does that give me access to those springs as well?

Lots of lazy people in the business, sad but true. Mostly an artifact of flat-rate pay instead of hourly, also true and also sad.

No, the springs are tiny leaf-springs form-folded inside the female pins. They put pressure on the male pin to assure good electrical contact. If a spring gets weak or collapses, the male pin can literally bounce around in the hole. When you do a pin-fit check, your safety pin is serving as an analog for the male pin and you're making sure the spring exerts some pressure on it. That's why you're feeling for it to "drag" when inserted or removed, and also why accessing the back side where the wire is crimped won't tell you anything.

[Dedpul]

Yep, just looked at a few videos so I have a better idea of what to look for. I think I have a pretty good idea now. Will update tomorrow or this weekend when I get some time to check them.

[Dedpul]

Starting to look at the pins, but i realized when i first start up the car, the O2 Sensor shows 0.2V consistently until the car is warmed up, once warm is starts to have those breaks in voltage.

[VStar650CL]

They all sit flatline until the heater warms them up and the cat is lit. That's normal. The ECM doesn't even look at it until the engine is warm and above idle.

[Dedpul]

I checked resistance on both the blue and pink wire. Good resistance and pins seemed to sit well. Tested Ohms for both cables as well and got 0.3 Ohms

[VStar650CL]

Has to be something. Some of the spikes in the oscillations you captured while driving are simply too fast for any process in the sensor to cause, unless the internal ceramic is broken. So if you're sure the first sensor was doing exactly the same thing, and you're sure it isn't pin-fit or wiring, then it has to be the ECM by process of elimination. If it has a cold or cracked solder joint internally it can cause that sort of behavior, it's just that cracked solder in an ECM is pretty rare. Hitachi's QC on that count is very good, so that's a "blue moon" kind of failure.