What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (2024)

There you are driving down the highway minding your own business when all of a sudden a fault code appears. It may be a good code or it may be one that will ruin your day. You just never know but you need fault codes to protect your huge investment in your truck or RV.

When you see this code it means “This code sets when the Aftertreatment Control Module (ACM) detects that the Selective Catalyst Reduction (SCR) NOx Conversion efficiency is low.” We will get to how to fix it shortly.

To learn more about this code and how to fix it, just continue to read our article. It has the information you want to know about so you know the right action to take when it appears.

Code SPN 4364

How To Fix Code SPN 4364 FMI 18

What is SPN 4364 FMI 18?

What Does Code SPN 4364 Mean?

Can I Drive With SPN 4364 FMI 18?

How To Fix Code SPN 4364 FMI 18

What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (1)

According to the Detroit data sheet we linked to above, you have about 18 steps to take before being able to clear this code. The first step is to connect your Diagnostic tool to see what other codes have been triggered.

The second step is to turn the ignition on but leave the engine off. This is the standard step you will find throughout the different codes and their solutions. Steps 3 to 7 are all about finding other codes and fixing them first.

If this code does trigger other fault codes for other parts, you need to clear those codes and fix any real problems before moving on to solving the trouble this code tells you about.

At step 8 you can turn the ignition off before you proceed to solve this code. Step 9 have you using the DEF test strip A000585 to see if any diesel fuel or oil has contaminated the DEF tank.

If it has, then you are supposed to go to this link to get the procedure to clean the tank. If it hasn’t, then you move on to using the refractometer from DEF Test Kit W0605 89001900 and check the urea percentage.

If the percentage is between 31 and 34% then you move on to the next step. If not, then you are to clean and flush the tank and replace the contents with new DEF fluid. After that, you confirm the repair.

If it is, you move on to the following steps including turning the ignition on again. Each step after 10 will have a place where you can verify the repair and stop the process.

At some point, you will have to do a parked regeneration. If that does not get the NOx level up to 70% you will have to send the information you have to the customer support center and wait for more information.

All the details are at that link above on pages 2 and 3.

What is SPN 4364 FMI 18?

This is supposed to be a catch-all code for anything to do with the NOx system in your vehicle. It is hard to pin down the problem as you will soon see. According to the Detroit data sheet, this code refers to the following:

This code sets when the Aftertreatment Control Module (ACM)detects that the Selective Catalyst Reduction (SCR) NOx Conversionefficiency is low”

What caused this code to be triggered for one owner was a loose exhaust manifold bolt. That was on the #4 cylinder and it had worked its way loose and finally disappeared.

This seems to have led to or was the result of a gasket failure around that same cylinder. After replacing all the gaskets and bolts, this code eventually went away. You might see it once or twice after the repair but that was for cleaning itself out and not for a real problem.

When we say this is a catch-all code for the NOx system, it is because there are quite a few sources that would trigger this code. The following are only 4 suggestions according to the data sheet:

- Contaminated DEF

- Incorrect concentration of urea in the DEF

- Biased NOx sensor

- Excessive DEF build-up in the exhaust

You may have to search for a while before you find the actual source for your triggered code.

What Does Code SPN 4364 Mean?

What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (2)

What this code is referring to mostly is your soot level. You may have an exhaust leak that allows the soot to build up somewhere and when it does you get the code.

Some people have suggested replacing the NOx sensor for this particular area of your engine but that is not always the right fix. Some owners have done that with no positive results. If it is the sensor that is at fault, these are the two that would fail on you- the SCR inlet NOx sensor and SCR outlet NOx sensor.

This is and isn’t a severe warning code. It will depend on several factors to take it to the severe level and usually, a parked regen will clear the problem and the code.

But as you can see by the information in the above section, this code is not restricted to the soot issue. You could have mistakenly put diesel fuel in the DEF tank or even a little oil got into the system.

Sometimes just flushing the old DEF out and replacing it with a new one after cleaning the tank, will solve the problem. The second link will take you to the instructions on what to do if the DEF is contaminated by diesel or oil.

Can I Drive With SPN 4364 FMI 18?

Yes, it is possible to drive with this code triggered. But you may not get that far down the road. Your traveling distance will depend on the amount of soot that has built up.

If it is low, then you have more than enough time to get to a mechanic or dealer to have the problem solved. If the soot level is high, you may have to endure a derate.

To do a successful regen, you do have to get the code cleared through one of the many steps listed above. Make sure to check the NOx sensors first. Even though there are other possibilities, you want to make sure they are in top shape before you move on to the other possible sources.

If you drive the situation will only get worse and the soot will continue to build up. Soon your vehicle will be reduced to 1000 RPM if you do not take care of it right away.

When it comes to NOx sensors, they are expected to last around 200,000 miles. This is not a part you have to change that often to keep your engine running smoothly.

Then, this code could be triggered by a low-quality DEF. It happens as many owners want to save money so they buy the lower quality versions and then mess up their engines because of it.

These are not the only parts that may trigger this code but even if it was something else, your performance may only be affected if there is a soot build-up.

SPN 4364 FMI 1

What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (3)

Since the FMI 1 code is tied to the SPN 4364 code, you know it is referring to your NOx system. In this case, this code means:

This fault code sets when the Aftertreatment Control Module (ACM)

detects that the NOx conversion is lower than a calibrated threshold”

In this case, there are over 20 steps to take to clear the code. The first two will be the same as the FMI 18 code and steps 3 to 8 direct you to fix and clear any other codes that may have been triggered at the same time.

You will also have to use the test strip and test kit to detect any contamination by oil and diesel as well as to check for the urea level. Step 12 has you turning the ignition on again but not the engine and steps 13 to 22 will have different solutions where you can verify the repair and be on your way.

You can get all the details at this link from the Detroit data sheet. This code’s solution steps also refer you to the second link above in the case of any oil and diesel contamination.

SPN 4364 FMI 17

This may be a code that is not listed in most data sheets for fault codes. The reason for that absence is that this may be in the advanced diagnostic version of fault codes.

This advanced diagnostic system provides a more accurate troubleshooting process and is preferred over the traditional troubleshooting processes. All the code means is “When the Aftertreatment Control Module (ACM) Detects Poor Selective Catalyst Reduction (SCR) NOx Conversion Efficiency” (source)

The possible sources would be but not limited to:

- Contaminated DEF

- Incorrect concentration of urea in the DEF

- Biased NOx sensor

- Excessive DEF build-up in the exhaust

- Improper DPF maintenance

- Over temp after treatment

This code seems to have about 27 steps you could possibly take before the code is fixed and cleared. Those steps are outlined at that link and that website seems to have copied a data sheet from the Detroit Diesel company.

We could not find the direct link to that data sheet. When you go to this data sheet make sure to read and understand the different notices and notes in between the steps.

They carry important information and we point them out because there are quite a few listed there before you get to the repair steps.

SPN 4364 FMI 31 Cummins

What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (4)

Cummins has its own set of fault codes that will relate to the SPN and FMi systems. In this case, the Cummins code is 5655 and it has to do with the following parts: “Aftertreatment 1 SCR Conversion Efficiency - Condition Exists. Amber light and NOx conversion across the SCR catalyst is too low.”

The result of this code is possible reduced engine performance. The possible sources for this code are but are not limited to:

- Malfunctioning after treatment diesel exhaust fluid dosing system.

- Exhaust system leaks

- Malfunctioning SCR catalyst

- Degraded, diluted, or incorrect diesel exhaust fluid

- Diesel exhaust fluid deposits in the decomposition tube.

- For a unit that has come back into with repeat failures consider the possibility that the customer is not using Ultra-low sulfur Diesel fuel.

Unfortunately, the Cummins data sheet from this link does not provide any troubleshooting steps for you to follow. But the data sheet does say:

It is necessary to use the "Reset All Faults" command in the recommended Cummins electronic service tool or equivalent to clear this fault and extinguish the amber CHECK ENGINE lamp and/or Malfunction Indicator Lamp (MIL).”

Troubleshooting For The Cummins Fault Code 5655 SPN 4364 FMI 31

We did find the steps you are to take on another link and you can read all the details of what you are supposedto do here. In the limited space left we can only list the steps and you would need to go to that link for specific instructions:

1 Fault Code 5655 requires that ALL solutions be performed

2 Check for primary fault codes

3 After treatment diesel exhaust fluid is contaminated

4 aftertreatment exhaust system leaks

5 Leaks in the after treatment diesel exhaust fluid dosing system

6 Aftertreatment Diesel Exhaust Fluid Doser Pump Override test

6.1 After treatment diesel exhaust fluid dosing valve is malfunctioning

7 Aftertreatment SCR System Test

7.1 After treatment diesel exhaust fluid dosing system test failed

7.2 Aftertreatment intake NOx sensor failed

7.3 Aftertreatment outlet NOx sensor - Inspection

7.4 Inspect both after treatment NOx sensors

7.5 Aftertreatment SCR Catalyst Test Failed

8 ECM calibration revision history check

Some Final Words

Fixing these SPN fault codes can be a bit tricky as well as lengthy. That is if you are skilled enough to handle the problems. Once you figure out the codes the rest is a matter of skill and time.

What Is And How To Fix Code SPN 4364 FMI 18 (FMI 1, FMI 31) (2024)

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