Cummins DEF System Problems: 6 Most Common Issues Highlighted

There are an increasing number of cases of Cummins DEF system problems with diesel engines. While on your camping trip, you may have experienced these diesel exhaust fluid system issues. I am going to go through six common DEF-related problems and tell you how to fix them. Let’s begin!

Cummins DEF System: A Basic Intro

Diesel Exhaust Fluid (DEF) is a type of additive and safe chemical that, at a rate of 32.5% water and 67.5% water, is specifically manufactured to maintain a low freezing point of 12 degrees Fahrenheit.

This fluid can damage SCR injectors and catalysts, impurities are tightly controlled and urea, which is commonly used in fertilizers, cannot be used to create DEF.

Cummins Diesel Exhaust Fluid Sensor Problems

In 2016, the Environmental Protection Agency (EPA) mandated that all new diesel engines must have a sensor designed to detect the concentration level of DEF. So the DEF system is composed of:

Some of these sensors had a short lifespan, and this was usually due to the design of the particular chassis, such as the Spartan chassis, where the DEF head was close to the hot engine exhaust system and circulated with hot engine coolant.

Three fault codes may be displayed if the sensor chip fails::

1. Cummins Fault Code (ERROR 3868) SPN 1761
2. FMI 9 (CUMMINS ERROR 4677),
3. SPN 3031 FMI 9 (ERROR 4572).

6 Cummins DEF System Problems Troubleshooting

Keeping up with regular DEF maintenance is important for the good running and emissions of an engine. That said, it’s worth knowing the problems that may arise.

1. Managing Your DEF

Handling DEF is an essential factor to consider as to its effectiveness and shelf life. Succeed the below guidelines for proper handling of DEF:

Take Care About Storage Place

Diesel Exhaust Fluid should be stored where it does not come in contact with direct sunlight, as this can cause it to degrade more quickly.

Don’t Store It In Too Much Cold Temperature

DEF starts to freeze at 12 degrees, so storing it in a more excellent environment is recommended. DEF can expand to about 7% when frozen if left at lower temperatures for too long. Hence, it is crucial to store DEF away from freezing temperatures as much as possible.

Keep It In A Container, Instead Of Bottles

Purchasing a container instead of multiple small bottles is recommended to ensure that you always have enough DEF on hand and that it stays at optimal quality.

This way, you can have a larger supply of DEF, but all stored in one container and away from direct sunlight.

2. Contamination Problem With DEF

DEF is a compassionate solution and can quickly become contaminated if mismanaged. Hence, it is essential to take extra precautions when handling DEF.

How To DEF For Contamination?

The way to check for contamination is to check the urea levels in the DEF filter tank. If the urea levels are lower than expected, it could indicate that the DEF has been contaminated.

Precautions To Prevent From Contamination

To prevent contamination:

3. Mileage Issues

One of the most common issues with Cummins DEF systems is related to mileage problems. It’s been reported that sometimes a vehicle speed goes through significantly lower mileage when using DEF.

How To Fix This Issue?

For this, you should:

4. Diesel Exhaust Fluid Crystallization

DEF Crystallization can occur when too much DEF is added to the system. A faulty DEF pump may cause this, plugged DEF lines, or the use of hard water for topping up the DEF system.

Effects Of Crystallization On System

Let’s look at the different effects of crystallization on your system.

1. Crystallization of DEF can cause the system to become clogged and reduce the engine’s efficiency.
2. The contamination can lead to an increase in exhaust emissions and a decrease in the fuel economy.
3. If left untreated, crystallization can also damage the fuel injectors and other engine components.

How To Avoid DEF From Crystallization?

To prevent crystallization:

5. DEF Dilution

Adding too much water when topping up the DEF system or SCR catalyst with an injector nozzle can lead to dilution and crystallization, making the fluid ineffective. This idea is a common problem in diesel fuel engines, resulting in decreased performance and increased emissions.

Affect On DEF Tank

When the DEF fluid is diluted, the engine’s control unit will detect a drop in concentration and display a warning message on the dashboard.

How To Fix It?

The only way to fix this issue is to replace the entire DEF tank. Succeeding the manufacturer’s instructions when refilling the DEF system is essential. Adding too much water can easily lead to dilution and crystallization.

6. DEF Freezing

When it comes to DEF freezing, it is not a big issue if it is in its storage container. This event is because it can quickly thaw with no damage. However, if DEF is freezing in the system during cold weather, this idea can cause severe issues with the SCR system.

Troubleshooting

Understanding what can go wrong with the DEF freezes and the design inside is essential to learn proper troubleshooting techniques. DEF that freezes in the system can cause blockages and lead to corrosion.

Ways To Solve This Problem

Follow these tips to fix this issue:

Common Problems with Cummins DEF and How to Test for Them

Here, I will explain the different possible issues with the DEF system along with their testing methods.

1. Test For Crystallization

Testing for Crystallization of DEF is a common problem, and it builds up over time. This can lead to decreased performance and fuel efficiency in your Cummins engines.

Different Ways To Test It

There are a few ways to test for crystallization and ensure the health of your DEF.

1. The most common field and lab testing methods include visually inspecting exhaust piping and DEF injectors for the presence of crystallization, testing DEF for evidence of minerals, and confirming DEF quality during delivery or in bulk storage.
2. You can use ICP Spectrometry or XRF Spectrometry to test DEF for evidence of minerals.

2. Testing for Dist / Metal Contamination

When inspecting your DEF, you should check that it appears clear and free of dirt or metal debris.

Test Procedure

Let’ know more:

3. Urea Concentration Test

When testing the urea concentration of your Cummins DEF scr system, it’s crucial to stay within the required parameters.

4. Testing for Other Fluids

Testing for other fluids should be done regularly to ensure the proper performance of the DEF system.

A Comprehensive Way To Fix the 5 MPH Derate

The 5 MPH derate causes the engine to become limited to a top speed of 5 miles per hour. A failed component in the system causes this fault and must be addressed before the vehicle can regain its full speed capability.

What Are the Common Failures Involved?

Common failures that can cause the 5 MPH to derate include:

1. Failed DEF doser valve
2. Ran out of DEF fluid
3. Inlet and Outlet Nox sensors failed, not making pressure
4. EGR system malfunction causing NOX efficiency problems
5. DEF pump failed, not making pressure

How To Fix It for DEF Pump?

To fix the 5 MPH derate:

FAQs

Concluding Thoughts

Overall, Cummins DEF system problems are common and can lead to severe problems if not fixed promptly. Understanding the basics of the Diesel Exhaust Fluid and how to troubleshoot and test for potential issues is essential. Caring for your Cummins system ensures it runs smoothly and efficiently for many years.

By staying informed and attentive, you can keep your DEF system running smoothly and avoid costly repairs in the future. What are some other Cummins DEF system issues you have experienced? Let us know in the comments below!