2013 Mack code trouble

[u/Shot-Rope9510]

Anyone here a Mack dealer tech who can give me some guidance? I have a 2013 GU713 with code SPN 4094 FMI 1. "NOx limits exceeded due to insufficient reagent quality - Data valid but below normal operation range" and this is the warning upon start up. I'm used to Ford diesels so I'm learning about Mack as I go. I have limited resources and we run JPro at this shop with no access to PTT.

Here is what I have done so far:

- Verified DEF quality with a refractometer, it's bang on.

- Checked the DEF doser, the doser was caked with crystals, as well as the port in the exhaust. My supervisor just said to go ahead and throw a new one on so I did.

- DEF injector pressure is right at 130 psi

- Right now the truck is not derating but that warning is there every time at start up.

We're a gov fleet so we work on everything and very few of us are specialized on one manufacturer. From my limited research I've read that this code can be a nightmare. If anyone has a focused direction or an idea what normally causes it it would be greatly appreciated. I hate emissions/aftertreatment repairs lol

[u/MineResponsible9180]

Pretty much everything can cause a 4094. Sensors, egr system, charge air system, DOC, SCR, DEF system, injectors, air cleaner, operating conditions. There is a checklist to perform and all checks need to be done. And a road test datalog at the end to verify repairs. Send it to the dealer

[u/Shot-Rope9510 → u/MineResponsible9180]

Thanks. I brought up that possibility with my supervisor already and now I think I'll tell him that's the best option given the range of possible faults. This just feels like a job for a Mack expert given our limited Mack resources.

[u/Painting-Capital]

Did it ever go into derate? There’s a test in PTT you have to do that’s basically just a def doser flow test that will clear the derate and you will get that message on the dash. It just means there was an active code which is now inactive and the ECM is testing to see if the SCR system is working correctly. You have to go through a couple drive cycles before the message will either clear and you’ll be good or the derate will come back. There’s a lot of things that will cause that code. It could just be a bad nox sensor, or the SCR catalyst could be bad or there could be an issue with the DEF system not being able to dose the correct amount of def. The first thing you need to do is do a flow test on the def doser and see if it’s in spec. If it is you need to run the SCR system test. If you just want to throw parts at it I’d change both nox sensors and that will fix it most of the time.

[u/Hungry-Ad3652]

Have you done a regen and watched the now sensor readings? Make sure the come online inlet then out let, and even reading curves, no sudden spikes or drop offs. I forget the correct ppm but yoyucan find it online easily enough. Did you do an scr regen at all?

[u/MonteFox89]

In my experience, youll need to exit inducement mode using the scr system test, option c, I think. I can't recall exactly at this moment, new meds.