Fault Codes Explained

A modern diesel engine is a very complex device. Over the many years that they have been used there have been steady increases in power, reductions in fuel usage and significant reductions in harmful pollutants. Some claim the exhaust of a modern diesel engine can actually be cleaner than the air going into it!

These improvements have required more and more sophisticated control systems. At the heart of the Cummins engines is the Electronic Control Module or ECM. It performs a number of important tasks and among them is continuous component fault monitoring. Whenever the key is turned on the ECM checks on the status of dozens of components and it continues to keep tabs on all of them while the engine is running. If it detects a fault, it evaluates which parameter is not correct and what the nature of the fault is. Some of these faults are minor and the ECM just stores them for future analysis. Some of them, like the emissions controls systems, are important enough to alert the operator to the presence of a problem and if the problem persists, the ECM will force action by reducing performance until the problem is resolved. This is called an Inducement or Deration. Unfortunately the ECM in this case is not able to distinguish a real problem that needs to be resolved from a false alarm caused by the failure of the very component that monitors the DEF supply.

All of these faults are reported in a standard format and use a few acronyms. The description of which parameter needs attention is called a Suspect Parameter Number or SPN Number and they are usually a 3 or 4 digit number. There is also information about the general nature of the fault. These are called Failure Mode Identifiers or FMIs. FMIs are a 1 or 2 digit number and each FMI number has a specific meaning. For instance a problem with SPN 1761 with FMI 9 indicates a problem with the DEF Fluid Level and the nature of the problem is an Abnormal Update Rate.

That’s enough background for you to understand generally what these fault codes are all about. Now for the specifics of what this means for the DEF sensor problem.
In the unlucky event that your coach is having a DEF sensor failure the first indication that you will see is the appearance of 3 very specific faults and the illumination of 1 or more warning lights. The lights that may be activated on the instrument panel are the amber Check Engine Light (CEL), the yellow Malfunction Indicator Light (MIL) and eventually the red Stop Engine Light (SEL). Sorry but engineers do love their acronyms. Where you will see the codes and other information varies and you should consult your Owners Manual or contact your coach’s Customer Service Department for how to display yours.

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

If all three of these fault codes appear more or less at the same time, then it’s virtually certain that the problem is that your DEF sensor has stopped outputting any data at all. The “Abnormal Update Rate” message just means that the ECM has not received any valid DEF data in a certain amount of time. It’s Abnormal because it is not there at all.

After installing the DEF Simulator the ECM diagnostics system will clear most fault codes and warning lights soon after the next key on event. However EPA regulations call for certain codes, notably the SPN 3031 code, to complete 3 consecutive 5 minute long engine operations without error before it will allow the codes to be cleared.

After installing the Simulator, usually you can just start the engine and idle for 5 minutes 3 times in a row and the codes will be gone the 4th time you turn the key on. Some versions of the ECM software will allow an external device like a code reader to clear the codes immediately but some versions don’t. Either way all warnings should clear themselves eventually so don’t let it worry you.

Please Note. If you DO NOT have ALL THREE of these codes then you may have a problem the Simulator can’t help with. That includes fault codes relating to any other DEF/SCR or emissions related codes including DEF pumps, DEF injectors and anything to do with the DPF System or Regeneration. The Simulator is a one trick pony and is not a panacea for all emission systems problems. Think of the Simulator as being like a “donut” spare tire. In a pinch it can get you out of a dangerous situation but it’s not a substitute for the real thing.

We strongly urge that if you have the failure described above that you use the Simulator to help you safely get to a repair facility where you can have the failed DEF sensor repaired with new OEM parts as soon as practical.




18 Comments to Fault Codes Explained

  1. JBS says:

    I’m wondering if it would be good idea to purchase and carry one of these simulators or readers that you mentioned? ?This way if the DEF sensor is the culprit all can be cleared and you’re on your way until a new chip arrives to replace the faulty one. Thoughts?

    • Archer2 says:

      We recommend that if you elect to build one of these Simulators that you check it on the bench with a multimeter very carefully to verify that your wiring is correct. That no wires are touching each other or anything else, there are no shorts or mistakes and that you got no errors or unusual messages while loading the software. Then put it away unless you actually encounter a failed Sensor as described with the 3 specific codes. Then and only then should you connect it in place of the failed OEM sensor. At that point you have nothing to lose. This is NOT a panacea for all emissions-related potential faults. We have complete confidence the software will work as described but we have no control of any errors you may have made in assembling the hardware and wiring. So treat it like a “donut” spare tire. it will get you out of a jam but it is not a substitute for the real thing. Good Luck.

  2. Lawrence Dedrick says:

    I believe I read somewhere that programing is downloaded and installed on the simulator.
    What site is the download available from?
    Is there a Mac version of the program?, for us with MacBooks.
    Is a USB all that is needed for the download?
    My apologies for possibly having you repeat instruction, but with all the reading I have done it becomes confusing where I have referenced material.
    Thank You

    • Archer2 says:

      Hi Mr. Dedrick. What you are going to need is to pick a circuit board you want to use. As of right now you have a choice of 4 different hardware setups. They are 1) Copperhill Arduino DUE with Dual CANBUS and extended power option. The benefits are that no soldering is required. The cable connections are done with simple screw terminals. The disadvantages are that the board is expensive at $150 and they can be difficult to find in stock. Although this is also the most powerful one of the selections that power is largely a wasted for this application.
      2) and 3) Arduino Mega2560 or Arduino UNO Either is fine. It’s just a matter of which you can find in stock and how much they cost. Both also require an additional piggyback board called a SeeedStudio CANBUS V2. Including the Seeed either should be at or less than $50. The disadvantage is that the Seeed wiring interface is a DB9 connector which can be difficult to wire because it is a very compact space to work in but it also doesn’t require soldering.
      4) Seeed CanBed Development Board. This is the newest to be tested. It is readily available from several suppliers. It has a screw terminal wiring interface and it currently costs about $20 total. No additional boards required. The downside is that the wire terminal block must be soldered onto the board. It is only 4 pins and easily done even for a novice solderer. It has a couple of quirks in how the USB connection works during programming but if you follow the instructions carefully it’s no big deal. It is currently my favorite and it’s only the size of a credit card.
      Next you need to download the program. There is only one installer package that covers all hardware choices. The instructions and links can be found in this website in several places, Including the Build It! Section and the Quick Build sections. Right now it is only for Windows PC but a Mac version is due any day now.
      Right now you need a Windows PC with an available standard USB port. The PC is only needed to connect to the DSS board via USB cable and to run the installer program ONE time. Once programmed, the boards will retain their programming for years (like 20 to 100 years) even without power. Double check the info for your hardware to see whether the right USB comes with it or to confirm what kind of USB you will need.
      All that’s left is for you to verify what kind of connector is needed to mate with your vehicle’s wiring harness as there are a couple of different ones used by different chassis manufacturers. This website also has instructions for the two most common ones for Spartan and Freightliner chassis.
      Everything you need to know and do is described on this website just check the right hand margin for links to the most popular pages.
      Good Luck

      • Lawrence Dedrick says:

        Thanks so much for your reply. What I purchased was what was posted on the quick build list. I called copperehill and was told their Arduino Based ECU Development Board with Dual Can Bus interface (JCOM.ECU.DUE-X) was the proper device to buy for the DSS build. It looks just like the one displayed in the quick build. I do realize there will be a waiting period due to demand. Looking forward to the build and having a peace of mind if ever needed.
        Thank You again

      • John says:

        How do you run the Seeed CanBed Development Board on 12v?

        • Archer2 says:

          I’m not 100% sure what you are asking but I’ll take a shot. The Seeed CanBed components on the board (the microcontroller chip, CANBUS Interface chips and their supporting components) natively run at either 5Vdc or 3.3 Vdc. The external power is applied to the Vin connector from the vehicle and can be any DC voltage from about 20V down to about 8V. The Seeed CanBed board comes with an on-board DC to DC switching converter/Voltage Regulator chip that conditions the Vin down to 5V and then then a different on-board regulator drops the voltage down to the 3.3 volts for those components that need it.
          Does that answer your question? May I ask why you asked?

          • JR says:

            Thank you, I was asking because if you use Arduino DUE with Dual CANBUS you have to use power extender, I mistakenly thought that Seeed CanBed Development Board was also 3.3v.

          • Archer2 says:

            That makes sense. Thanks for the question.

  3. Don says:

    I own a 2013 Freightliner equipped Tiffin Motorhome and have started to experience a very intermittent DEF temp error 3031 FMI 2. It has cleared 2x on its own. My concern is it may put me on the side of the road before it can be troubleshot. Has anyone had success installing one of these kits on an older DEF system?
    Thx, Don

  4. Pardon me for my inexperience, but are these SPN #’s industry standards that every scanner will recognize and display? Are these specific to Cummins, or Freightliner? Also, what scanner should I purchase, if you could give a recommendation?

    • Archer2 says:

      Generally speaking PGNs and SPNs are defined in the SAE J1939 standard for Heavy Duty trucks. There are some reserved PGN/SPNs for proprietary use by manufacturers but that’s not an issue here.
      I don’t have an opinion on scanners but I know that some people swear by the BlueFire product and I think there are other similar products as well. They are not exactly code scanners in the normal sense but they are quite a lot more sophisticated and flexible but also way more complicated.

  5. Terry Lee Nay says:

    Thanks so much for this solution!!! Please HELP….In attempting to program the “CANBED” Board option, I am getting the following error. I tried deleting the download DEF Simulator Download Files v0.2 (x32) and reinstalling to my C Drive, still no luck. Turned off firewall and antivirus before attempting. Re-Tried Install steps 1-11 and get this each attempt, (windows 10 machine, what am I doing wrong????):

    Microsoft Windows [Version 10.0.19042.1288]
    (c) Microsoft Corporation. All rights reserved.

    C:\Users\Terry’s Laptop>cd\avrprog

    C:\AVRProg>program canbed 5

    C:\AVRProg>echo off
    canbed selected

    avrdude.exe: Version 6.3-20190619
    Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
    Copyright (c) 2007-2014 Joerg Wunsch

    System wide configuration file is “C:\AVRProg\avrdude.conf”

    Using Port : COM5
    Using Programmer : avr109
    Overriding Baud Rate : 57600
    AVR Part : ATmega32U4
    Chip Erase delay : 9000 us
    PAGEL : PD7
    BS2 : PA0
    RESET disposition : dedicated
    RETRY pulse : SCK
    serial program mode : yes
    parallel program mode : yes
    Timeout : 200
    StabDelay : 100
    CmdexeDelay : 25
    SyncLoops : 32
    ByteDelay : 0
    PollIndex : 3
    PollValue : 0x53
    Memory Detail :

    Block Poll Page Polled
    Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
    ———– —- —– —– —- —— —— —- —— —– —– ———
    eeprom 65 20 4 0 no 1024 4 0 9000 9000 0x00 0x00
    flash 65 6 128 0 yes 32768 128 256 4500 4500 0x00 0x00
    lfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
    hfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
    efuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
    lock 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
    calibration 0 0 0 0 no 1 0 0 0 0 0x00 0x00
    signature 0 0 0 0 no 3 0 0 0 0 0x00 0x00

    Programmer Type : butterfly
    Description : Atmel AppNote AVR109 Boot Loader

    Connecting to programmer: .avrdude.exe: butterfly_recv(): programmer is not responding

    avrdude.exe: butterfly_recv(): programmer is not responding

    • Archer2 says:

      Terry’s issue was that he didn’t see the step unique to the CanBed board that requires you to determine which USB port is briefly assigned immediately after pushing the reset button on the CanBed board, and to use that port number in the programming command line. He also was briefly trying to use a “charger-only” USB cable but he figured that out on his own pretty quickly. I’m just posting here for the benefit of others who may run into the same problem.

  6. Rick S says:

    I don’t have a Windows computer. I bought a Arduino Due and connected it to my macbook and I’ve used the IDE to install the example “blink” sketch. I’m wondering if we can get hold of the sketch source code as that would make it easy to load via the IDE regardless of Windows or OSX.

    • Vic Chanko says:

      Hi Rick. The short answer to whether we will provide the source code to the public is flatly “No”. The issue is that while the code as designed and written DOES NOT disable or defeat any emissions system, it could be abused in such a way as to allow such abuse. So the decision was made from the very beginning that the code would be distributed as a binary runtime only. So I’m afraid that, even though we have generally bent over backwards to make this DIY project as easy as possible for users, this is going to be a take it or leave it proposition. Sorry

  7. Dwyer Stringer says:

    How do I test the assembled simulator? My DEF Sensor was replaced and currently have no codes, hate to wait IF it happens again and find out my Simulator does not work.

    • Archer2 says:

      About all you can do is make sure that your coach key is off and unplug the OEM sensor and plug the DSS in its place. Turn the key on and watch for the DEF level gauge in your instrument panel to begin indicating 75% full (it doesn’t matter what the actual level was). If you have no codes or warning lights after 5 minutes you can start the coach and let it run until you are confident that there are no fault codes (10-15 minutes should be fine).
      Then shut it down and swap your OEM back in and check that no codes show up with the key on/engine running.
      That’s about it.

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