Check Engine - Code 3521 FMI 11

[swaff54]

So, we were leaving the west suburbs of Nashville this morning headed to Dallas. Figured a 3 day trip arriving at NIRVC for some work on Wednesday. Body repair and windshield replacement.

As we were heading west on I-40, the check engine light came on just before we were going to merge onto I-40/I-24. I had been at Cummins a couple of months ago here, so I took that exit instead and am currently sitting in their parking lot.

We're showing Code 3521 FMI 11. From what I've read, it is related to DEF. I've decided to overnight here in the Cummins parking lot. When we were here back in September for engine and generator service along with caring for the fuel rail recall. They allowed us to overnight, since they couldn't get both the service and recall issues cared for in one day.

If anyone as any insight on what Code 3521 FMI 11 is specifically, I would appreciate any input.

[Archer2]

Sorry to hear about your trouble. SPN 3521 is DEF Fluid Property, Root Cause Unknown. It means either the DEF tank contains an unknown fluid (water, diesel fuel, windshield washer solution, etc.) OR the DEF Quality Sensor (aka “DEF Head”) has failed or is failing.
If you are certain that the tank contains only fresh, high quality DEF fluid and you are also certain that it has not been accidentally adulterated with some other substance then you are likely going to need a DEF sensor replacement.
If the service center can’t get a replacement immediately then you should ask them to apply the Cummins TRP to reprogram your ECM to be able to continue operating your coach until an OEM replacement can be installed.
If neither of those things can be done and you verify that it is your DEF Sensor that has failed then DM me and I will send you a DSS loaner to get you back on the road.

[swaff54]

Monday morning, the folks at Cummins were able to check the codes and determined that I had 1 of 2 problems. Either bad DEF or a bad DEF head. They did a test of the DEF in the tank and determined that the DEF was good meaning that I have the dreaded bad DEF head issue.

In the meantime, NIRVC reached out to me with a possible temporary fix. Cummins reset the codes prior to my departure from their shop in Nashville. I then drove to NIRVC's Nashville location in La Vergne. The check engine light and code came on again during that short drive.

On Tuesday afternoon, we left NIRVC Nashville with the temporary fix and we're on our way to NIRVC in Lewisville.

Kudos to the folks at NIRVC for their great customer service.

Please don't ask what the temporary fix is. I don't want to reveal anything that shouldn't be public. If you've followed the DEF head issue at all, you probably already know what the fix is.

Also thanks to Archer2 for reaching out with the offer of a DSS loaner.