What Is Cummins Code SPN 3720 FMI 15? (Helpful Guide)

When you get a specific SPN code, you can see up to 21 FMI sub-codes illuminated with that one SPN number. There are a few more than 21 FMI codes but most are reserved for future use by the SAE. This can make repair work difficult.

SPN 3720 FMI 15 refers to Aftertreatment 1 Diesel Particulate Filter Ash Load Percent - Data Valid But Above Normal Operating Range - Least Severe Level. The Cummins equivalent is supposed to be 5383 but it is not listed on the comprehensive Cummins fault code list.

To learn more about this fault code, just continue to read our article. It has the information you want to know about so you can get to the heart of the problem quickly and make the appropriate repairs. This code may not cause a derate.

What is The SPN 3720 FMI 15 Code?


This code is “Aftertreatment 1 Diesel Particulate Filter Ash Load Percent - Data Valid But Above Normal Operating Range - Least Severe Level” but the problem you will have if you are only using the Cummins comprehensive list is that it is not there.

You will have to go to other sources or resources to get all the information about this code before you start making your repairs. In basic language, this code is telling you that the “Diesel Particulate Filter Has Reached the End of its Service Life.”

You will have to replace this filter to be able to clear this code. After replacing the filter, you will then have to perform the Ash Accumulator reset using DiagnosticLink.

To do the replacement, you will have to find this filter. It is inside the exhaust system and it may not be a DIY part you can replace. Check your warranty and owner’s manual for instructions before you proceed with the repair.

The good news is that you should still be able to drive with no effect on your engine’s performance. But you should get the filter cleaned or replaced before too long. The derate may come in when the filter is full of particulates and the line gets clogged.

SPN 3720 FMI 15 DD15


The only thing different about this code is the letters DD and the number 15. When you see this code, you are told to either clean or replace the DPF filter. If you do not want to have them cleaned or replaced, you can do what is called baked.

The baked procedure is something you would have to discuss with Detroit Diesel or a qualified mechanic. The location of this filter is in what is called the One Box and you may have to replace some exhaust clamps, clips, and screws.

To make the repair easier and give you better access to the DPF filter, you can remove the One Box completely. However, to complete the repair, you will need the DDDL software to input the DPF’s serial number and reset the code.

There is some information you should know about and this information comes from this data sheet:

Regarding DPF ash accumulators, EPA07 vehicles calculate DPF ash levels only by miles, not engine hours. Therefore, large amounts of PTO use with PTO Dosing enabled will eventually generate DPF pressure codes well before the normal full ash level distance (for example, 300,000 miles on an EPA07 DD15) and resulting fault code SPN 3720/FMI 15 – DPF Ash Clean


EPA10 and later vehicles calculate DPF ash levels based on the actual vehicle duty cycle, and will therefore correctly calculate the time when to activate fault code SPN 3720/FMI 15 – DPF Ash Clean Request.”

If you are not able to crawl under your vehicle to access this part, leave the job to a qualified mechanic. This is an easy repair for them.

SPN 3720 FMI 14


There is not much information on this code at all. The data sheet is only 2 pages long, if that, and it does not contain very much information. Here is what the data sheet has to say:

DiagnosticLink users: Please update the troubleshooting guides in DiagnosticLink with this newest version. To update the tool troubleshooting guide, open DiagnosticLink and from the Help – Troubleshooting Guides menu, select the appropriate troubleshooting manual, then click Update”


ACM Reported Ash Mileage is Lower Than MCM Stored Value

Check as follows:

1. Connect DiagnosticLink ®.

2. Turn the ignition ON (key ON, engine OFF).

3. Select Diesel Particulate Filter (DPF) ash accumulator from the actions drop-down menu.

4. Choose Aftertreatment Control Module (ACM) replacement option, then select set ash volume button.

5. Verify that the ACM value has changed in the DPF ash accumulator window and that the 3720/14 MCM fault is no

longer active. ACM will change to a value that should be within 5% of the MCM displayed volume within 5-10 seconds of executing the routine. Clear all faults and release vehicle.”

When you look at the complete list of FMI codes, all you will see beside #14 are the words “Special instructions”. In other words, you may have to talk to a qualified mechanic or the company directly to find out what you should be doing for the repair.

The more comprehensive SPN code list has the 3720 fault code listed but it only includes FMI 15 & 16. If you get 16, then you can expect to have your engine derated at some point. It is a moderately severe code level.

SPN 3720 FMI 15 only tells you that it is a cleaning request and that it is the least severe level. No mention of a derate in its content. When you see FMI 14 talk to a mechanic to see what they say. You may still be able to drive to the nearest service center without any problem.

Have the filter checked out to be sure you do not move up to FMI 15 or 16.

Aftertreatment 1 Diesel Particulate Filter Ash Load Percent


We checked a variety of data sheets and none of them provide an answer to the question of what is the filter’s ash load acceptable percentage or anything similar. They just talk about what will happen and how to resolve the problem.

The different sheets just state the basic ‘the filter needs cleaning or replacing’. It would be hard to put a percentage on the DPF filter as that would be hard to monitor. The sensor just knows when there is too much ash in the filter.

The conditions that trigger this code are: “The engine monitors the aftertreatment diesel particulate filter (DPF) differential pressure sensor.

When the aftertreatment diesel particulate filter (DPF) differential pressure is above a maximum value at the end of an aftertreatment regeneration the fault code is activated.”

As you can see, no percentage is given that will trigger the code. On your dash, all you should see is the maintenance lamp illuminated telling you there is a maintenance task waiting to be done.

As we said with the DD15 code, you will need special diagnostic software to clear the code. The command you need to use is “Aftertreatment Maintenance Filter Installation”

Either the OTR Diagnostics or the Cummins Insite diagnostic tools are needed to perform this task.

Cummins Special Instructions For SPN 3720 FMI 15


We came across this data sheet that has 5 pages of special instructions to fix or resolve this code issue. The most important piece of information this data sheet has is “Fault Code 5383 requires that ALL solutions be performed”.

Even if you find a resolution to the problem, you must perform all the solutions given to you for this problem. You can take that up with Cummins if you have the time.

Like other fault codes, you will have to resolve any other ones that are related to 5383 or SPN 3720 FMI 15 before tackling the solutions for this code. What Cummins has to say is this:

Before troubleshooting this fault code, troubleshoot any fault code that is active or has more than one inactive count within the last 25 engine operating hours from the following list:

- Aftertreatment differential pressure: 1879, 1881, 1883

- Aftertreatment DPF: 1922”

This comes from page 2 of the data sheet and there are 5 pages of instructions to follow. If you are not sure about what to do with this information do not be afraid to ask your local mechanic who works on this problem.

Some Final Words

This is not a serious fault code to be given. In fact, it is one of the easier and less expensive ones to have to deal with. Needless to say, if you see this code, do not delay the maintenance work for too long.

If the FMI code switches to 16 or 0 then you will have to deal with a derate and that is never any fun. Take care of the codes quickly so they do not develop into more serious problems.

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