What Is Fault Code SPN 3251 FMI 16? (Cummins, Freightliner)

That is the way it is with new systems or any system for that matter. Once you understand how they work, they become very easy. The same can be said for finding what fault codes mean. Once you understand how everything works, you get to the source in seconds.

For this code, the equivalent Cummins code is 1921. It means- Aftertreatment 1 Diesel Particulate Filter Differential Pressure. The data is valid but above the normal range.

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 understand what the problem is and how to fix it. Some codes are a DIY fix and others are not. Knowing these codes will help you tell the difference.

What is Fault Code SPN 3251 FMI 16?


For the Detroit Diesel engines, there are 3 of these codes. While they all say SPN 3251 FMI 16 what we noticed was there was an extra set of code letters after the FMI 16.

The first set of letters is EPA07 and it stands for- “This diagnostic is typically Diesel Particulate Filter (DPF) Pressure Out of Range High. This fault code sets when the DPF outlet pressure is greater than 30 kPa (4.2 psi) for more than 10 seconds.”

To fix it you have to attach the diagnostic link and you either have to disconnect the exhaust behind the DPF and clean it out, or you have to replace the DPF outlet pressure sensor.

The second set of letters for this code is EPA10 and it is the same problem as 07. However, the repair is different. There may be a build-up in the Selective Catalyst Reduction (SCR) and it needs to be cleaned out, or you replace the same sensor as 07.

The third set of letters is GHG14 but everything is the same as EPA07. This link will give you far more details than the Detroit Diesel data sheet supplies. The fix should be done by a dealer in this case.

Part of the fix will be a regeneration once the soot has been removed. You should only see an amber warning light illuminated when this code is set but an engine protection derate may occur.

Freightliner Code 3251

While codes are not always numbered the same, the problem is the same. With Freightliner, the FMI16 is referring to a plugged DPF, which is the filter inside the exhaust system.

This should trigger a moderate to severe level code and you would have to do a regen once the problem has been resolved. There are several sources for this clogged DPF in your exhaust system.

Those sources include but are not limited to the following parts- turbo, EGR, or fuel problems. You may or may not be able to diagnose this issue and find the correct source. It might be a dealer-only type of fix if this code returns after a regen.

You can try to hook up your own diagnostic reader and find the problem. But the repair may be beyond your skill set due to the location of the part. The location for the DPF is inside the exhaust system and it may take special tools to reach it as well as replace it.

What the regen is supposed to do is to remove the built-up soot. If it doesn’t then you may have trouble with those parts mentioned earlier in this section. Also, look for any other codes that may have been set when this one was set.

SPN 3251 Aftertreatment 1 DPF Differential Pressure


This can happen in the most inclement weather. One owner had it take place at -25 degrees F and after he did a forced regen and ungelled his fluids. One source for this problem may be condensation.

The condensation can get inside the exhaust system and freeze. This will create a false reading. The fix is something you can do yourself and you will need to take the differential pressure tubes off and clean them.

Also, when it is cold out, you should warm up the sensor to double-check its reading. When it is cold it can give a biased reading. Then reset the soot level but this is only done dependent on the current soot level reading. The sensor looks like this:

The filter is inside the exhaust so you should not see it here. If this does not solve your problem, then you may need to talk to a skilled mechanic and see what he has to say.

This explanation is for a 2013 Kenworth t270 paccar px 6. This problem and solution may or may not apply to other Kenworth models or other RVs or truck models.

Unfortunately, there are just too many models to deal with. This explanation is only to get you on the right path and a possible fix for your fault code.

Where is The DPF Pressure Sensor Located?

This sensor, as shown in the image above, is right on the diesel particulate filter. The filter, as we have already said, is in the exhaust. Hopefully, your sensor looks exactly like the one in the image above.

If not, it may look like the ones in the following image:

This DP sensor is different on different makes and models. But its location should be similar in those different makes and models. The sensor should be mounted on the aftertreatment assembly.

You should find it above the heat shield protecting it from the heat of the emissions system. With different designs, you may not find it right away. It may be in the engine compartment for the same reason.

Your owner’s manual may have an exploded parts diagram that will show its exact location for your specific make and model of vehicle. If not, then you can always contact the dealer or the company itself to get that location.

Just make sure you know which design you are looking for. They are not a universally designed part.

Why Does The DP Sensor Fail


There are a couple of common problems for this part failing on you. The first source would be the wires that connect the sensor to the ECU. Those wires can get cracked or melt due to the extreme heat in the area or the road vibrations knock them loose or damage the wires.

A second source for this part to fail would be the soot. The hoses can become clogged from this soot just like the DPF does. That is why you need to clean those hoses or tubes when you see this code.

While it does not sound like a major problem, it can be. If the soot remains, the sensor cannot be accurate in its pressure measurements. This issue can result in catastrophic DPF damage and eventually the engine.

While you may hate seeing fault codes, these codes are designed to keep you from paying extremely large repair bills.

SPN 3251 FMI 0 Cummins

This is one of two SPN 3251 codes on the comprehensive list we provided in another article. Its Cummins fault code is 1922 and it stands for:

Aftertreatment 1 Diesel Particulate Filter Differential Pressure- Aftertreatment Diesel Particulate Filter Differential Pressure -Data valid but above normal Operating Range”

What all that means is-- “Cummins fault code 1922 becomes active when the soot load of the Diesel Particulate Filter (DPF) has exceeded the recommended limits. To protect the engine, the ECM activates the power derate.”(source)

The last line is what you should pay the most attention to. Expect to lose performance and power when you see this code. When you do your own passive regen for this problem, the soot is supposed to be burnt off and the life of the inlet of the filter and extends its life somewhat.

The exception to this option is when you are doing nothing but pulling or hauling light loads. The average temperatures on the DPF may not be high enough to do a passive regen and you may have to use a stationary regen to get the problem solved.

The ECM makes the final soot level decision by monitoring both the inlet and outlet pressure of the filter. Depending on the pressure, the code is triggered. When fault code 1922 is set, you should also see the red stop engine light illuminated as well.

The Source Of The 1922 Or SPN 3251 FMI 0 Code


This information is taken from the same source as linked previously:

1. Wiring harness- Incorrect wiring harness pin installation. Consult the wiring diagram and check the wires.

2. Operating conditions- The engine spends too much time on light load conditions, causing insufficient DPF temperatures which prevent passive regeneration to take place.

3. Engine problems- If the engine has malfunctioned, it is possible that excessive soot is created, causing the DPF to get blocked.

4. DPF ash loading- Burned soot leaves ash behind. Ash is stored in the DPF. Excessive ash in the DPF causes blockages.

This diagnosis may be above many owners' mechanical skill sets to fix or find. Make sure you have help just in case you do not find the right source for the problem.

The link above has the troubleshooting information you need to know to fix this problem. You will have to go through each step to repair the problem and clear the code.

There are 9 steps to follow and each one is quite detailed.

SPN 3251 FMI 2

This code is telling you that the DPFDP is above or below the desired level. You may or may not see it on a Cummins engine but the FMI 2 code is not listed on the comprehensive Cummins fault code sheet.

This code may be only for the 2010 + MaxxForce DT, 9, 10, N9 & N10 (ESN 3,300,000 and later) engines. There are about 5 possible steps you can take until the problem is solved and the code is cleared.

The first step is to check your DPF for the following problems- plugging, kinks, cracks, or other defects. That will include the tubes attached to the filter. The first fix for this step is to repair those defects and retest for the fault.

But there are two other solutions as well. The second one says to go to step 2 if there are no defects but there is high DPFDP is suspected due to differential

pressure spikes.

The third solution is to go to step 3 if the opposite is the source- low DPFDP is suspected due to rapid drops in differential pressure. You can read all the steps you need to take at this link.

SPN 3251 FMI 4

SPN-3251-FMI 4

The Cummins fault code number for this fault code is 1881 and it says:

Aftertreatment 1 Diesel Particulate Filter Differential Pressure- Aftertreatment Diesel Particulate Filter Differential Pressure Sensor Circuit - Voltage below normal”

The possible sources for this problem can be an open circuit somewhere or there is a short in the system. You may have a loose connection at the DPF pressure sensor. Or there may be some water or dirt that has got into the system and shorted the wiring a little bit.

This can be a DIY fix if you know what you are doing. Also, check for other codes at this time as well. There may be more than one.

Some Final Words

Finding the source and possible fix for each code becomes easier once you know the system. With our Comprehensive Cummins fault code list, it should not take very long to make the diagnosis.

Once you find the problem, you can then decide if you are able to fix it yourself or if you need expert hands to help you. Not all codes are this easy to repair.

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