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

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 2^nd gear to try to creep past that 5 MPH mark realizing after a few minutes that 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 uses ammonia to 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! 

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