Please Help. SPN-4364.

Not that this is your problem but when was the last time the DEF filter was changed?
Intake or exhaust leaks can cause problems. Exhaust leaks will most times have black soot.
Need: SCR temp in; SCR NOx in, SCR temp out and SCR NOx out. If the shop does not have the normal ranges from service data they could get that off another vehicle w/o codes. If the SCR NOx and SCR temp in are good then your engine is good with no leaks. There is only the DEF injection and SCR left. Diesel Selective Catalyst Reduction (SCR) - exhaust gas goes in reacting with the DEF and catalyst (metals) to reduce NOx. In a gasoline engine car the exhaust gases go into the catalytic converter, react with the metals (platinum, palladium...), to reduce NOx. Over time these metals wear off and there is not enough to do their job (reduced efficiency). Tests have shown that these converter metals are on the ground along highways.
Probably end up needing the SCR.

Below are a few pieces from an excellent article.


One of the more common issues that can create problems with modern engine aftertreatment systems is air leaks in the intake and aftertreatment plumbing. Leak testing should become part of your regular routine. “The best practice being used by large fleets is to perform a 10-minute leak test as part of routine maintenance,” “Because air leaks in the intake and exhaust system are the most common cause of aftertreatment failure and excessive maintenance, maintaining the seal and integrity of your intake and exhaust systems will give you the biggest payoff,” Developed in collaboration with International Trucks, the Redline Detection HD PowerSmoke replicates high-pressure boost load so the intake and exhaust systems can be tested for faults with the engine safely off. It can reliably detect high-pressure and low-pressure upstream faults, pinpoint exact locations and precisely identify failing components.

 

One person on this forum stated that he spent 18k on emissions/aftertreatment repairs to not fix the problem. Was not fixed until someone found a corroded wire/connection. A driver monitors oil pressure, coolant temp etc. with gauges on the dash. There is a normal range for everything including all the sensors on the truck. A shop that knows what they are doing needs to look at all the data especially what readings were at the point the code was set. And follow diagnostic procedures. Can't emphasize enough that it needs to be verified that the engine is operating properly before condemning anything else in the after-treatment system. A pressure test with either air only or air and smoke to check for intake and exhaust leaks would be a good idea at this point. Does not take much time, should not cost very much, no parts involved, and can rule out a lot of things. Realize this is all general and somewhat vague but can only do so much online.

 

Excellent question as the same one crossed my mind. It may be that something else (non aftertreatment related that does not set a code) goes wrong causing high emissions that the SCR can't handle and setting the code. The code could be a symptom and not the cause/problem. Take what happened with you NOx in sensor. The -80 to 1,000 and moving all over the place tells that it is bad. But no code was set. One should have been. So all the data needs to be looked at.

 

I did see that post. The smell says something is very wrong but is not specific enough to point to any one part.

 

This is from a Cummins bulletin last updated 2015 for Code 3582. Not specific to Maxx but gives you an idea of the process. Step 1 is check for codes and step 7 is SCR. Looks like you have completed anything I checked.

 

Adding this:
Some trucks have a diffuser, a metal plate with holes, that spreads out the spray from the doser. The person reported that the shop eventually found that the plate had corroded and fallen off.
Several cases of where the SCR near the doser cracked setting a code(s). The SCR was welded.
Wiring problems causing NOx issues.
So back to the data when the code was set. What's the PPM and Volts for each NOx sensor (in and out)? What was the data for the DEF?