FAQs

What is a Diesel Exhaust Fluid (DEF) Sensor Simulator (DSS)?

A DEF Sensor Simulator is a device that replaces a failed DEF Head and sends simulated DEF level, quality, and quantity messages to the Cummins ECM so it believes everything is operating normally.

Who designed the DSS?

The DSS was developed by a group of motorhome owners who met online in 2021 to develop a workaround for the DEF Head failures that were becoming commonplace.   Due to supply issues caused by COVID replacement DEF Heads were not readily available, thus the  development of the DSS.

The primary technical architects included:  Flyboy013, Archer2, RadarEng.

Additional contributers included: JP, PhlSeattle, Voltdoc, and redbaron73.

Can I build one myself?

Yes.  Build instructions can be found here.

Is this capability licensed?

Yes.  A licenses had been granted for individuals to build their own utilizing the published firmware.  This is for individual use.  The license does not allow for commercial use of the firmware.  DSS units cannot be sold utilizing the firmware.  The only company authorized, is DEFSIM, LLC as it is owned by the author of the firmware.

How do I know if I need one?

When the DEF Head fails, it stops transmitting DEF sensor messages to the ECM.  The ECM responds by generating diagnostic trouble codes which causes the check engine light to illuminate.  The codes that are generated are:

There are 3 specific SPN numbers along with their Failure Mode Indications that are associated with a DEF sensor failure:

    • SPN 1761 FMI 9 Aftertreatment 1 Diesel Exhaust Fluid Tank Level-Abnormal Update Rate
    • SPN 3364 FMI 9 Aftertreatment Diesel Exhaust Fluid Quality-Abnormal Update Rate
    • SPN 3031 FMI 9 Aftertreatment 1 Diesel Exhaust Fluid Tank Temperature – Abnormal Update Rate

Which motorhomes does this work on?

This capability was developed for motorhome with Cummins engines with a CM2350 Engine Control Module (ECM).  It was later tested on motorhomes that have the CM2450 ECM.  The digital DEF Head were required starting with engines manufactured on January 1, 2016.  There are 2016 motorhomes that have engines built in 2015, so you need to verify.  Typically you can just verify that you have one of the two connectors.

Will I still have to add DEF?

Yes.  This is not a DEF delete capability.  It's only purpose is to send message to the ECM indicating that there is fluid, along with temperature and quality values.  If you run out of DEF, other errors will occur as the DEF dosing unit will be unable to inject DEF into the exhaust.

Is it legal?

Yes.

I see there two different devices.  Which one do I need?

Most chassis manufacturers use the Deutsch DT04-4P connector for the DEF Head.  Freightliner uses their own connector.  It is important before ordering a device to verify which connector you have.  You may have to cut some zip ties to access the connector.

How will I know if my DEF Head has failed?

The check engine light will be illuminated and you will have 3 diagnostic trouble codes.  In particular: SPN 1761 FMI 9, SPN 3364 FMI 9, and SPN 3031 FMI 9.

I see others are also selling these.  Are they legal?

No.  No other individual or business has a license to sell products using the licensed firmware.

Are the devices you sell any better than what others are selling?

Yes.  The units being sold here have various unique features. Some of the are:

    • The case is custom designed with four standoffs to secure the circuit board in the case.  Other are using generic project boxes and are using adhesive to secure the board.
    • Each wire has a ferule on the end of the wire.  This avoid a strand from one of the four wires from touching another wire causing a short.
    • The case is made of ASA rather than ABS material.  ASA is the superior choice for an outdoor circuit board enclosure because it offers exceptional UV and weather resistance. While it matches the strength and heat resistance of ABS, ASA replaces a rubber component in ABS that degrades in sunlight, preventing the enclosure from turning yellow, becoming brittle, and cracking
    • Each device is tested by connecting it to a simulated ECM to verify that it works as designed.

Why is your price so low?

The team that developed the original DSS did so to help the community, not to line our pockets.  Our goal has been and continues to be to help our fellow motorhome owners.  While many folks are gouging customers by charging upwards of $600, my goal is still to help the community.