Your Cummins has a 5 MPH DEF Derate (SPN 5246). What now? (2024)

You’ve heard the same story over and over, maybe even experienced it yourself.

You just crossed the bridge into Canada and your 2013 Peterbilt 389 with a Cummins ISX CM2250 truck was turned off at the border checkpoint. When you start your truck back up you notice a red stop engine light and your DPF light is flashing. The truck carrying your precious load is now in a critical state of emergency. You pray that it’s not in the dreaded 5 MPH derate…

So, you hold the clutch down and put it into 2nd gear to try to creep past that 5 MPH markrealizing after a few minutesthat your truck will not budge. So, you crawl to the shoulder only to find that now you can’t even proceed driving.

Unfortunately, we hear this story on a daily basis from our customers. It’s something we hear all the time because this is what happens when the truck detects a fluke in the system or from a malfunctioning component.

What is a DEF derate or an aftertreatment derate?

A derate means that the program inside the engine computer limits either the power or vehicle speed. A derate is designed to protect you from causing engine or DPF damage. A derate can be caused by various sensors or systems. However, when it’s a specific 5 MPH derate then you can be certain that the problem is related to the emissions, aka the aftertreatment system.

What components make up the emission system that controls the 5 MPH derate?

DEF Fluid – The tank with the blue cap holds DEF Fluid. This has a level sensor and a quality sensor to make sure the concentrations are in allowable limits. If you have bad DEF fluid, this can cause DEF quality issues and can put you into a derate.

DEF Doser Valve – Regulates the injection of the DEF fluid into your SCR Catalyst.

DEF Pump Assembly –This is the heart of your DEF system that pumps the DEF fluid throughout the DEF system. If this fails, you will go into a derate immediately

NOx Sensors, both inlet and outlet sensors –When the sensor detects much NOx in the exhaust stream, it tells the SCR/DEF system to inject more urea, which usesammoniato reduce emissions levels in your system.

DEF Control Module – This module controls the operation of the emission system. The DEF Module and Engine Control Module (ECM) are in direct communication to make sure the system is operational.

ECM – The DPF system and the regeneration process is controlled by the ECM on a Cummins truck. So, the DEF module + ECM make up for controlling your entire operation.

The dreaded fault code that causes the 5 MPH derate!

This fault is related to the “SCR Inducement” which is what regulates your truck to this derate.

  • Cummins Fault Code – 3712 or SPN 5246 FMI 0
  • Notification – Red Stop Engine Light On
  • Information – Aftertreatment SCR Operator Inducement – Data Valid But Above Normal Operating Range – Most Severe Level. Critical SCR related fault codes have been active for an extended period of time and require immediate attention.
  • Immediate engine power derate. Vehicle speed will be limited to 5 miles per hour or 8 km per hour.

How to temporarily override this 5 MPH derate on a Cummins engine?

Unfortunately, we don’t have a tip or trick to share on how to do this on a Cummins powered truck. The only way we have found is to clear the fault codes with a dealer level service tool to allow you to drive to a service shop. If you have the OTR Diagnostics, then you will be able to reset the system yourself anytime anywhere. This is a more cost-effective solution to get you to a dealer or shop. You can learn more about OTR Diagnostics here.

How to fix this 5 MPH derate?

You need to see what caused the “SCR Inducement Code” to come up in the first place. A failed component is usually what triggers this code.

Common Failures

  • Failed DEF doser valve
    • Associated fault code: SPN 5394
  • You ran out of DEF fluid
    • Associated fault code: SPN 5392, SPN 1761
  • Inlet and Outlet NOx sensors failed, not making pressure
    • Associated fault code: SPN 4094
  • EGR system malfunction causing NOX efficiency problems
  • DEF pump failed, not making pressure
    • Associated fault code: SPN 4334, SPN 4339
  • DEF module has failed or DEF harness failure or no power to DEF module causes DEF gauge to be empty and showing datalink error and SCR malfunction.
  • The DEF / ECM could also need updating to eliminate ghost codes.

Is it safe to drive with a derate?

We recommend seeking service immediately. Driving with a derate may cause permanent damage to your engine or emission system. Be cautious when driving with an active derate and get into a service shop as soon as you can to figure out what the issue is.

Can you do updates to the emission system?

Yes, updates are recommended if they are available. It’s recommended to see if you have any updates available and to do them if so because this can remove any bugs or issues. However, please note that this isn’t a fix for all your problems or ghost codes, but it’s good practice to have the latest updates.

We hope this blog post helps you if you are ever stuck in a derate!

Untilnext time! 👋
Stay safe, stay healthy & be blessed.

Your Cummins has a 5 MPH DEF Derate (SPN 5246). What now? (2024)


How to get cummins out of derate? ›

When your truck is under Derated, you have to do the following step by FCAR truck scanner if there is not physical part failure:
  1. Go Diesel Engine, select Cummins, it will show couple DPF/DEF/Aftertream related codes. ...
  2. Under Cummins main menui, selction Action Test to find Forced Regen Option to start Forced Regen.

What causes a Cummins engine to derate? ›

A derate is designed to protect you from causing engine or DPF damage. A derate can be caused by various sensors or systems. However, when it's a specific 5 MPH derate then you can be certain that the problem is related to the emissions, aka the aftertreatment system.

What is the fault code spn 5246 fmi 0? ›

The 5246 is an inducement fault. This is just an indicating fault that states that a derate is present. Just like the 4094 fault. In order for this fault to go inactive the system must go thru an evaluation process.

What happens when a diesel engine derates? ›

The DPF works under extreme conditions, collecting the ash that results from burning diesel. The engine can derate when a needed regeneration does not occur. When an engine derates, it can cause downtime by leaving the vehicle in an undrivable state or “limping mode” where it's only operable at low speeds.

How do I force my Cummins to regen? ›

Initiate Regen:
  1. Navigate through the Cummins Insite software to the section related to DPF regeneration.
  2. Look for options related to "Forced Regeneration" or "Manual Regeneration." These options may vary depending on the version of the software.
  3. Follow the on-screen prompts to initiate the regeneration process.

How to clear Cummins fault code? ›

Using a code reader tool, connect to the ECM and find the “fault codes” tab. The displayed codes can generally be clicked on one by one. Another option is to select “erase all faults” and then follow the onscreen instructions. At the end of the procedure, the ignition key should be turned off.

What is one of the most common problems in the DEF system? ›

Dirt / Metal Contamination: Contaminated DEF can cause abrasion of the DEF pump. Dirt, rust or tank scale can occur with improper DEF storage or handling (e.g. res-using disposable DEF containers).

What does DEF warning light mean Cummins? ›

Illuminated An illuminated DEF Lamp is an indication that the DEF level is low. This can be corrected by refilling the DEF tank with Diesel Exhaust Fluid.

What does SPN mean in diesel? ›

A Suspect Parameter Number (SPN) is a specific code used in the automotive industry to identify and diagnose faults codes in electronic control units (ECUs) within vehicles.

What does SPN mean on a code? ›

Next, we see SPN which stands for suspect parameter number, this is used to identify the specific component or condition that is triggering a fault. In our example, we see SPN 3216, when looked up this SPN shows that there is an issue with the Aftertreatment Intake NOx sensor.

What is the failure mode indicator FMI? ›

Failure Mode Indication (FMI), as part of the J1939 standard used in heavy-duty vehicles, functions by closely monitoring system components. When a fault occurs, FMI generates a precise code that identifies the specific nature of the issue, much like an advanced version of a 'check engine' light.

Is engine derate bad? ›

Derating sometimes is done intentionally when you want to prolong the engine's life and avoid substantial wear or damage. However, in some applications, such as a power generation facility, unwanted derating reduces the energy production which leads to lost revenue potential.

What is a DPF reset? ›

Often shortened to “regen,” a DPF regeneration is the act of the system burning off collected particulate matter and turning it into ash. Eventually, the DPF system needs cleaning when ash levels are too high but regens significantly extend the amount of time before a technician intervention is necessary.

What causes engine derating? ›

As the ambient temperature increases beyond designed operating conditions, engine derating begins, decreasing its efficiency. For example, if an engine is designed to operate at 30°C, and the ambient temperature reaches 40°C, the engines can experience a reduction in power by as much as 5-10%.

What to do when a truck derates? ›

In order to get it out of derate, you can try running a forced back to back regen with a scan tool and monitor the outlet nox levels, if it is acceptable it will get out of derate. You also can do the derate reset with a scan tool to remove it temporarily.

What does it mean to have an engine derate in 3 hours? ›

Typically with a fault that states "engine derate in 3 hours," you'd be looking at an aftertreatment system fault. Typically something like an aftertreatment temperature sensor, a nox sensor, a DEF issue or something wrong with the DPF or SCR.


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