MX 13 EPA 13 Faults

Hi all, any help on this would be appreciated; even speculation is welcome. 2015 KW T680 MX 13 EPA 13, last 8 FJ449173.

I currently have fault codes SPN 4364 FMI 18 (catalyst under efficiency), and SPN 5112 FMI 9 (turbo code?!). Recently I also had temporary codes of 5109, and 3821 (can't recall FMIs) but they're no longer active. I just had the EGR cooler flushed, BPV rebuilt, the DPF baked, fuel rail relief valve replaced, and I cleaned the doser valve with a wire brush.

Any thoughts? Truck is running great otherwise. I know all of those run off of the same data line, could it be a CAN/wiring issue? Simple NOx sensor? Trying to avoid a trip to the dealer.

Edit: 500k miles. TONS of work done on this thing within the last year. ($25k+) Getting ready to trade it in for a Cascadia and DD15 if these constant codes keep up.

 

Alright, so no additional codes but I'm now limited to 20psi boost unless engine braking, which allows full pressure.

Anybody know where the chassis grounds for this part of the harness is?

 

Thank you!

I assume there shouldn't be a problem if I ran another ground wire from the cab ground to the battery posts, frame, engine, and turbo actuator, right?

 

I very, very much appreciate you looking into this and giving me some workable information!

The DEF filter was replaced roughly 50k ago, so a new one couldn't hurt. The code ended up clearing last night (day 2 of running [~20hrs run time] after cleaning the crusty doser), DEF consumption has decreased by 1/2 gal per 600mi. Calculated @ first fill last night. If the code returns I will replace both NOx sensors as they are AFAIK original units.

In the course of the night the ECU decided to grace me with full boost once more but the code remained active. During the aforementioned fuel stop I snipped the zip tie at the actuator, the wiring sleeve had been worn through but the wires it contained seemed in decent shape, even at the connector. I wriggled the cable around and re-zipped it so a different portion of the sleeve was making contact with the actuator. Not sure if that did anything useful but when I fired up the truck again I was overjoyed to discover that I had no check engine light for the first time in weeks! I ordered some water proof cable sleeving and plan to peel back the original, as you suggested, to have a good look.

Thank you!

If only fixing my oil consumption could be as simple, lol. I suspect valve guide seals as my truck is right at the recall cut off, but a thicker oil helps and only goes through a gallon every 30k.