Diagnosis for 0420/0430

[Greeno237]

I guess I've been (mostly) lurking here for over 5 years now. I want to thank everyone who's contributed to this forum over the years, it has been a great resource for wrenching on my Pathfinder.

I'm hoping for a bit of insight on whether I should be worried about my catalytic converters or not.

I have an '04 R50 with A/T, and it has been a real treat to own, I had no idea these things were so reliable, she rolled past 400k (kms) last year sometime, and now I'm hoping to see it get to 500,000

Since I bought it, the CELs been on due to a 0462 DTC, and the diagnostic process led me to a dead end when I couldn't figure out how to repair the PCB in the instrument cluster. I even wrecked my original board because I'm not very good with a soldering iron (I pulled up one of the traces). Luckily I managed to pull a cluster from an '03, and that has served me well for the last 4 years.

Recently I saw the video linked in this thread post6854380.html so I yanked the cluster out again and reflowed the solder on those 4 resistors. That seems to have fixed the fuel gauge, though I need to 'calibrate' the needle.

Before I pulled the cluster out last time, I grabbed the codes and saw U1001, P0420, P0430, P0462 and potentially one more? I should've written them down but I didn't.

After the cluster repair, I changed the oil/filter and replaced the oil cooler o-rings. Then I did some washing under the hood, mostly trying to clean off the old oil around the cooler, but I did hit the topside lightly with the wash wand. After this my CEL came back, showing U1001, P0420 and P0430. I cleared these codes and have taken multiple short drives (10-20 minutes each) to see if they will come back. So far, I've got U1001 with no CEL(as expected), and no more DTCs.

Is it possible that the U1001 code is caused by the '03 cluster? Should I pursue diagnosis of the U1001 code as outlined at EL-462? Should I follow the process for 0420/0430 diagnosis starting from EC-334? Should I just wait and see if any DTCs come back?

I recently grabbed NDS2 so I have access to some of the CONSULT II functionality, but not all of it. I can see the SRTs, I can log STFT & LTFT, as well as a bunch of other data that I'm generally not knowledgeable enough to interpret. Which is why I'm bringing the problem to the experts!

If I left out any important details, lmk and I'll fill them in.

[VStar650CL]

The P0462 was almost certainly from the bad fuel gauge circuit, and the ECM does "talk" directly to the cluster, so it's entirely possible the '03 cluster is telling it (or failing to tell it) something indecipherable. Since you got the original cluster working, I'd suggest seeing if the code will erase with the original connected. If so, then you know something is a little off with the comms from the '03.

The P0420/P0430 by themselves almost always mean the catalytic converters are shot. Under certain circumstances the rear O2's can "fool" the ECM, but in most cases there will be other codes in addition to the dead-cat codes. With all that mileage, I'd actually be pretty surprised if your cats weren't dead. If so, while there isn't as much risk of "cat inhalation" on an axial VQ as there is on some other models, it can still happen. So it isn't necessarily wise to drive around for too long with dead ones.

[Greeno237]

Oops, that was a bit ambiguous. I repaired the '03 cluster recently, I may be able to repair the original '04 cluster too, but that will take some doing as I have to reflow resistors and repair the damage I did. I don't mind doing that to see if it will clear the U1001, but I am more worried about the cats.

Should I just run through the procedures going forward from EC-334 to see if I can 'force' those codes to show up or just wait patiently? Can the fuel trims or O2 sensor voltages tell me anything about the state of the cats without waiting for codes?

Thanks for the help!

[VStar650CL]

You can pretty much evaluate it the same way the ECM does. First check the A/F-alphas (STFT) and LTFT to make sure there's nothing obviously out of wack with the mixture. If that's okay, take it on the highway and get the cats lit at a steady cruise. The ECM checks the sensors by watching both the voltage and timing of the oscillations, the cats by comparing the oscillation rates of the rears compared to the fronts. Healthy O2's should normally swing back and forth from about 0.3~0.8V at about 0.5 Hz during a steady cruise. Nominally the oscillation rate of the fronts should be faster than the rears by about 35% (rear rate / front rate = 0.75 or less). As the cats wear out there's gradually less difference, a totally dead cat will give you a 1:1 ratio because the cat is doing nothing and the O2 in the exhaust stream is identical on both sides.

[Greeno237]

Alright, after getting some driving data, I suppose my big question is, do the small oscillations of the second o2 sensor "count" or does it only count as an oscillation when it crosses 0.5V? From what I can tell, if the small ones "count" then it's pretty close to 1:1, but if the sensor has to cross 0.5V to be considered a cycle, then it is much closer to the 0.65 ratio. Here are both banks across the same 30s of pretty steady driving.
Bank 1:

Bank 2:

Is that the best way to get a look at this stuff, steady speed steady rpm?

[VStar650CL]

Driving at a steady cruise with the engine fully warm, or warming up and then holding a very high steady idle, are really the only ways to get a valid picture. Turning on the Cruise Control on an open highway gives best results, because it's hard to hold a high idle steady with your foot. Yes, the little oscillations on both sensors count, the reversal of direction is what the ECM looks at for purposes of the cats. I'd say yours look dead.

[Greeno237]

Well damn, obviously that's not what I was hoping for. So, worst case scenario, one of them takes out the engine? It's nice to know that's not a very likely outcome for these motors. Is it going to lose power and fuel economy until they get replaced?

Any recommendations on cats, brands to buy or ones to avoid?

Thanks again for the help.

[VStar650CL]

Even though the risk of inhalation is pretty small on a VQ, eventually one or both of them will probably clog up. Then you have a big performance issue. Any internal combustion engine is a glorified air pump. It dies when strangled, just like anything else that needs air.

For aftermarket, I've had good luck with both AP-Eastern and the high end Walkers. Between the two, I'd give the edge to AP-Eastern because I've never had a fit problem. I've had to tweak a couple of Walkers over the years. Bosal is good too, but I don't know if they're around anymore. Stay far away from China-cheap junk, I've seen several of them fail in very short order (and on one Sentra it actually took out the engine). 'Nuff said.

[Greeno237]

If I understand this correctly there are 2 failure states for cats, either the catalysts get degraded/destroyed or the matrix of honeycombs inside gets plugged up. Does catalyst loss/failure usually lead to a plug, and is that what tends to lead to inhalation?

I'm mostly trying to get a sense if I can check in on this thing with the scantool by watching the air flow, fuel trims, and calculated load at WOT. I've been reading a lot about diagnosis with fuel trims and the O2 sensors, and all of it lines up exactly with what you've said. Other causes would reveal themselves in the fuel trims at various RPMs, and those 2nd O2 sensors tell us everything else we need. If I've got the big picture correct, any significant restriction in the cats should start to "show up" as negative fuel trims at WOT as the blockage doesn't allow the correct amount of air through the system and the ECM will have to lean out the mixture to compensate for that. IS that right?

Is that a somewhat reliable way to "monitor" the cats for physical blockage? Or will anything like that show up way too late? I'd like to get another oil change or two out of this thing before I replace them, if possible. In Canada I don't have to worry about the CEL taking her out of service. Is another 4-7000 miles like this fairly low risk? Is there anything else I can do to reduce my odds of engine destruction until I replace the cats?

Walker P/N: 16343 and 16344 are these the "high end"? They seem to be the only walker fronts that aren't Cali versions. The only ones I can find, anyway.

I saw on another thread you mentioned ~2 hours per side, is that when all 6 bolts come out? I'm worried I'm going to have to torch/drill a bunch of them, they appear to be made of rust at this point.

[VStar650CL]

Rust never sleeps, crappy fasteners will always complicate any job. Yes, those labor times assume everything comes off cleanly. That certainly isn't a safe bet with your mileage in a Canadian environment.

Like I said at the top, axial VQ's aren't prone to inhaling the cats. That's a small risk. The risk of a clog is pretty high, but that won't destroy your engine, just your performance. It isn't always true about the STFT's going lean from a clog, that depends a lot on the ECM software. When the engine is choked, the MAF tells the ECM that the airflow is reduced and it will dial back the fuel in response, so what will principally change are the MAF readings and injector pulse widths, not the mixture. However, your ears and foot will tell you when a cat clogs badly enough to matter. The engine will start to act like it has a governor and produce a very distinctive howl at WOT, nothing else sounds quite like it.

[Greeno237]

Great, I'm glad I sort of understand the theory, bonus that it isn't that complicated to monitor in the real world. I've recently been fighting with trailing arm nuts/bolts, and you're damn right about rusty fasteners. I guess if this was easy we'd see a lot more vehicles hitting 400-500,000km