SPN 4364 FMI 18 solution for Cummins Paccar International Detroit

SPN 4364 FMI 18: NOx conversion efficiency low – The SCR system is not effectively reducing NOx emissions, which could be caused by a variety of issues, such as low DEF quality, a malfunctioning DEF injector, or a damaged SCR catalyst. We supply diagnostic laptops which are able to clear this SPN 4634 FMI 18 code on any engine you need, be it Cummins, Paccar, International, Detroit Diesel, etc. With our Caterpillar diagnostic laptops, you can work on your truck or equipment and save the money you would be paying the dealer! Check out the diagnostics page for more info or just contact us with what you need.

SPN 4364 FMI 18 diagnostic laptop to fix the code

Basic Toughbook laptop with the program for YOUR engine, a Diagnostic Link Adapter from only $1800! Please contact us for more info with what you need.

What is SPN 4364 FMI 18?

SPN 4364 FMI 18 is an engine error code that can cause a lot of confusion and concern for drivers and fleet operators. This code is related to the aftertreatment system of the engine and can indicate a variety of issues, ranging from a faulty NOx sensor to a malfunctioning DEF system. In this article, we’ll explore the causes and symptoms of SPN 4364 FMI 18 and discuss some potential solutions.

First, let’s break down what SPN 4364 FMI 18 actually means. SPN stands for Suspect Parameter Number, which is a unique identifier for engine fault codes. FMI stands for Failure Mode Identifier, which provides more specific information about the nature of the fault. In the case of SPN 4364 FMI 18, the FMI code 18 indicates that the fault is related to “Selective Catalyst Reduction (SCR) NOx Conversion Efficiency”.

The aftertreatment system of a diesel engine is designed to reduce harmful emissions and comply with emissions regulations. The SCR system, which is part of the aftertreatment system, uses a chemical reaction to convert nitrogen oxides (NOx) into harmless nitrogen and water vapor. The efficiency of this conversion is measured by the NOx sensor, which sends data to the engine’s control module (ECM). If the NOx conversion efficiency falls below a certain threshold, the ECM will trigger SPN 4364 FMI 18 and illuminate the check engine light.

SPN 4364 FMI 18 Causes

There are several potential causes of SPN 4364 FMI 18. One common cause is a faulty NOx sensor. If the sensor is malfunctioning or reading inaccurate data, it can cause the ECM to think that the NOx conversion efficiency is lower than it actually is. Another possible cause is a malfunctioning DEF (Diesel Exhaust Fluid) system. DEF is injected into the exhaust stream to help reduce NOx emissions, and if the DEF system is not functioning properly, it can lead to lower conversion efficiency.

Other potential causes of SPN 4364 FMI 18 include a clogged DPF (Diesel Particulate Filter), a malfunctioning EGR (Exhaust Gas Recirculation) system, or a software issue with the ECM. In some cases, the issue may be related to the quality of the diesel fuel or DEF being used, or to improper maintenance of the aftertreatment system.

SPN 4364 FMI 18 Symptoms

So, what are the symptoms of SPN 4364 FMI 18? The most obvious symptom is the illumination of the check engine light. In some cases, the engine may also go into derate mode, which means that its performance is limited in order to reduce emissions. This can result in reduced power, lower fuel efficiency, and other performance issues. In addition, if the underlying issue is not addressed, it can cause damage to other components of the engine or aftertreatment system over time.

So, what can be done to fix this code? The first step is to diagnose the underlying issue using diagnostic tools such as a scan tool or a diagnostic computer. This will help identify the specific component or system that is causing the fault. Once the issue has been identified, repairs can be made as needed. For example, if the issue is a faulty NOx sensor, the sensor can be replaced. If the issue is a clogged DPF, the filter can be cleaned or replaced.

In some cases, simply resetting the fault code may be enough to temporarily resolve the issue. However, it’s important to note that this is not a permanent fix, and the issue is likely to recur if the underlying problem is not addressed.

How to prevent it from coming back?

Preventing SPN 4364 FMI 18 from occurring in the first place requires proper maintenance of the after treatment system. Regular inspections and maintenance of the system can help prevent issues from developing and ensure that the system is functioning as intended. This includes regular cleaning or replacement of the DPF and DEF system components, as well as ensuring that the correct diesel fuel and DEF are being used.

In addition, it’s important to follow proper driving techniques and habits to reduce emissions and promote optimal performance of the aftertreatment system. This includes avoiding idling for extended periods of time, reducing unnecessary acceleration and deceleration, and maintaining proper speeds.


In summary, SPN 4364 FMI 18 is an engine error code related to the aftertreatment system of a diesel engine. It can indicate a variety of issues, ranging from a faulty NOx sensor to a malfunctioning DEF system. Symptoms include the illumination of the check engine light and potential engine derate mode. Proper diagnosis and repairs are necessary to resolve the issue, and regular maintenance of the aftertreatment system can help prevent issues from developing. By following proper driving techniques and habits, drivers and fleet operators can help promote optimal performance of the aftertreatment system and reduce emissions.

Panasonic Toughbooks for diagnostics

Panasonic Toughbooks are the strongest laptops in the world. They are a favorite of police & military forces around the world. The downside? High prices from the factory. These units cost as much as $3000-5000 USD! However, refurbished they are much more affordable. I supply a wide selection refurbished Toughbooks with a 6 months warranty. I customize both hardware and software to your precise needs! Please contact me if you got any questions or would like to order a unit.