Maine2500HD

Over the counter from Napa to my hand. Highly doubt counterfeit. The 1 hour applies to new vehicles (and in theory when the ECM/Battery has been disconnected long enough to reset.) I hadn’t heard of it either, but it came up on research, and explains why I could make the P0430 code go away for most of the day when I’d disconnect the battery, when it would otherwise reset regularly. The drive cycle is fairly specific and a GM thing, and is an over the road test at speeds/loads for a specific amount id time. In the grand scheme of things $800 ish for any pipe with all three Cats isn’t awful…. But I’m not excited to spend it just the same.

It doesn’t really take much for a defueling event duration to read/set it. I was watching it in Live data. It can be as simple as a slight/brief lift off the throttle. The ECM will not allow the code(a) to be set during the first hour-ish? Of run time after a battery disconnect. That is to allow for a break-in/run-in of cats when they are replaced. That’s why I could make it go away for a while. I’m seriously questioning if the NTK sensors are even spec’d right, or maybe were my boxed right? Had the right connectors but that doesn’t mean the sensors were right. They almost seemed like they wanted to run in a 2V range where it should only be a 1V range. I took all four back. It was wild the type of problems that they were causing. Entire bank 2 misfires, had communication errors between ECM and two different modules, varying voltage codes. Engine running in open loop for extended amounts of time (45+ min) Pretty nutty stuff.

When you clear the code (by unhooking battery, if that’s what you were doing) there is somewhere around an hour of “run time” where the ECM won’t set P0420 or P0430. That’s a provision to allow for the cat “break-in” or “run-in” procedure that is supposed to be followed after replacing the cats. So if you aren’t hitting that hour over three days, it won’t come on. If you are like me and go over that time in a day it comes back. For my P0430, if I use my scanner to clear the DTC it will just come back next time it looks for it (which is during defueling interestingly enough).

Well, I solved it. Garbage NTK sensors. I put all the original Denso sensors back in and the problem went away. I don’t know what’s up with the new NTK sensors but they were causing al kinds of crazy issues with voltages and they were so far out the truck was defaulting to Open Loop for hours at a time and running off of tables. When it would try to cycle back to closed loop it would stumble and misfire Bank 2 badly. It caused some weird “no communication” errors with a couple different modules when it was in misfire mode. fingers crossed, but the issue hasn’t come back since I out the original Denso sensors back in. I do think the P0430 will come back. Watching the upstream and downstream sensor graphs, it’s apparent that the cat isn’t 100% ok. There are times the downstream mirrors the upstream fluctuations, though not super often. The Bank 2 sensor also has a little more fluctuation than Bank 1 sensor 2. I did plugs and wires last fall and discovered that the Bank 2 components were all original at 120k but bank 1 had been changed. Was having misfires on bank two. I think that stress probably led to the degradation of the Bank 2 Cat. Planning on replacing it, soon.

I’ve since learned that when you disconnect the ECM, it will prevent the P0430/420 codes for roughly and hour of run time. This was by design to be able to allow for CAT break ins to be done without setting codes.

I did a full swap of all four sensors, codes and original behavior all keep coming back. Swapped some of the old sensors back in, and have moved new ones around, and none of the sensor movement caused a change in symptom. My first code that made me start down this road was a P0430, which still comes back intermittently. Second code was for Bank 2 Sensor 2. The shitting runny and flashing CEL didn't happen until I had all four new sensors in. Now it recurs regardless of the combination of new and old sensors and after watching voltages, they are all behaving like normal today. Diagnosis is going to be interesting because the failure is intermittent.

Ever find a cause?

Your drivability never suffers? I'm basically forced to reset the ECM sometimes because it stumbles, stalls, and flashes the MIL light and it's pretty much undriveable for a bit. It will sometimes snap out of it but not always. I'm impressed you've been able to tolerate it this long. Not knowing what it is or being able to diagnosis just irritates the s**t out of me lol

I think the CAT thing by the dealer is B.S. The strange part about my issue, is that I can make it go away for a day or so by disconnecting the battery. But so far it continues to come back when it feels like it. Hooked it up to a high end diagnostic tool briefly this morning, with no codes(after having unhooked the battery and resetting it this morning so I could drive it), and we looked at the graphical voltage data from all four O2 sensors and as expected there were no anomalies at all. Everything is functioning as it should. We cleared all past/existing codes in the system which is more than I could do with my tool, and basically set a baseline. Going to keep running it and see if it returns. So far I have almost 90 miles on it since the reset this morning and no hint of a code. I'm leaning heavily to a wiring issues somewhere with an intermittent short causing it. I took out my scope and checked a few grounds and they are clean as a whistle so I haven't disconnected any of those and chased them yet. I'll keep you posted. I really doubt that you'll find the issue to be your cats.

What did you find? I have nearly the identical problem with my 2014