What Is Engine Derate? All You Need To Know!

In general, a derate means that the car engine computer program is limiting the vehicle speed or power. It is designed to protect you from causing any engine or diesel particulate filter (DPF) damage.

However, engine deteriorating, aka derating, can be extremely beneficial in certain situations. It is enabling a prolonged engine life, especially preventing overheat.

Various sensors in the system can cause a derate. More specifically when the derate is 5 MPH you can be sure that the problem is directly related to the after-treatment system, aka the emissions.

Before the read check-engine light appears and your engine starts to derate, your onboard computer has attempted several programmed actions to clean the DPF.

Your car observation system is monitoring the amount of fuel passing through it, as well as the pressure and the temperature in the diesel particulate filter (DPF).

A programmed calculation is determining the actual restriction afterward and identifying the projected DPF restriction. The engine continually attempts to clean the DPF as you are driving down the road. If the DPF is not cleansed successfully, your yellow DPF light will turn on, and you will have to help in the cleaning process.

In that case, you will have two options. You can decide to change the mode in which the vehicle is operating so you can receive more heat into the exhaust, or stop the vehicle to perform an active regen. If an action is not taken at this point, the red light on your dashboard will illuminate and eventually, your engine will shut down or derate.

Intentional Derate

Sometimes engines can be intentionally derated! Intentional derate occurs whenever the manufacturer is asked by the customer to change the engine rating and lower the performance.

There are many reasons for customers to ask for this. Every vessel is designed for different and specific operations whose priority does not match with the manufacturer’s default configurations. Basically, the manufacturers can re-configure the default settings to provide the desired result.

The primary advantage is that the reduced thrust is cost-saving and increases engine life. The secondary advantage is that it is saving fuel under certain circumstances that may be possible to increase the maximum takeoff weight for a specific runway by using a reduced thurst profile.

Unintentional Derate

On the other hand, unintentional derating is more of an urgent situation, as we already mentioned. Here is another point of view:

When engines are rated, they are claimed to provide a certain amount of power for a specific time and exact conditions. These conditions and lifespan are taken under consideration and presented on all advertising brochures and sales strategies.

In general, every engine is designed to work best on a specific temperature and fuel. For example, if the engine is used in the right environment with the right supplements, it will last longer and be more reliable. If not, the engine will not provide the same amount of power and shorten its lifespan.

This is one of the biggest customers’ frustration as the recommended fuel and liquids are expensive and not all of the users can afford them. In that case, after a few years, the engine is starting to work harder and provide less power as before, and the result is a loss.

5 MPH Derate Explained

If you have a Paccar truck that is from 2011+ then you need to take a closer look and pay attention to your emission system! Keep reading and you will be prepared for any case scenario before a problem occurs.

You need to know right away that the emission system is complicated, especially for the Paccar powered trucks. There are two after treatment ECUs for these types of emission systems. One is controlling the DEF system, and the other is used to control the DPFand the after-treatment in sync with the engine ECU.

Many different components are making the DEF & DPF system. You need to be aware of all the limitations before you are stranded in the middle of the road.

If you have an issue related to the emission system, then sooner or later, you will enter the 5 MPH derate, which will be enabled by the ECU. You are now probably wondering how to remove the 5mph derate?” and this is precisely what we are going to discuss up next.

For this operation, you will need only a few high-level tools, such as the software called “Davie4” (dealer level) by Paccar. The service itself will be expansive because you will need to get your derated vehicle to the nearest dealer that has access to the mentioned software.

It is important not to let them fool you with their technical conversation! Ask right away for the “Davie4” software or if they can remove the 5 MPH DEF derate with any of their available dealer tools.

Lucky for you, OTR has a 5 MPH DEF derate tool for reset. The OTR reset tool for Paccar will reset the 5MPH derate at the dealer level, and it will give you the capability to perform these resets yourself for a significantly lower cost.

Now let’s see what the benefits for you are:

The OTR’s reset tool will completely clear the fault codes at a dealer level. That means that you will be able to replace any failed parts and check if the fault codes are in “Ghost code”. Then you can clear the CEL and check if it will come back eventually.

Most of the time, it is unlikely to come back unless there is an ongoing issue what the parts that you have replaced before, and you will need to check the system once again to locate any bad parts.

Most importantly, the rest tool will also reset the 5 MPG DEF derate. It will send the rest at the highest level dealer to make sure you won’t need to visit a repair shop or any service dealer. It will save you a lot of time and money.

You don’t need to find yourself stuck in a situation when you will have to trust someone else to resolve your problems. Equip your vehicle with OTR’s reset tool and prepare yourself for your journey. You don’t want to drive without this tool on or side.

Emission System Components Responsible for the 5 MPH Derate

• DEF Doser Valve – It is the component that is regulating the injection of the DEF fluid into your SCR Catalyst.

• DEF Pump Assembly – This is the heart of the DEF system that pumps the DEF fluid trough the emission system. Immediate derate is a result of failure!

• DEF Fluid – This is the tank with the blue cap holding the DEF fluid. It has level sensors and a quality sensor monitoring if the concentrations are within the allowable limits.

• DEF Control Module – This is a relevant module that is controlling the operation of the emission system. The Engine Control Module (ECM) and the DEF Module are in direct communication with each other, making sure that the system is completely operational.

• NOx Sensors Inlet/Outlet Sensors – These sensors are monitoring the exhaust steam. When they detect much NOx in the exhaust stream, they are requesting the SCR/DEF system to inject more urea, which is containing ammonia to reduce the emission levels in your system.

• ECM – The ECM on a Cummins truck is controlling the regeneration process and the DPF system. The entire operation is controlled by the DEF Module + ECM.

Fault Code That Causes the 5 MPH Derate

• Cummins Fault Code – SPN 5246 FMI 0 or 3712.
• Notification – If your red stop engine light is on.
• Information – If you notice a critical SCR fault code that has been active for an extended period of time it is necessary for immediate attention!
• Immediate engine derates – When the vehicle speed is limited to 5 miles/8 kilometers per hour.

Common Failures and How to Fix The 5 MPH Derate?

To resolve the 5 MPH immediate derate, you need to check the “SCR Inducement Code” that has appeared in the first place. A failed component is usually what is triggering this code, as we already discussed.

Here are some common possible failures:

• Run out of DEF fluid, SPN 1761, SPN 5392.

• DEF Dose valve failure.

• Inlet and Outlet Nox Sensor Failure, SPN 4094.

• When the DEF Pump is not making pressure, SPN 4339, SPN 4334.

• The ECM / DEF is possible to need updating to eliminate the ghost issues.

• DEF Modle Failure can cause a derate when there is no power supply to the DEF Module causing the DEF gauge to be empty and displaying an error to the Datalink and SCR malfunctioning.

Is Driving With a Derate Safe?

The recommendation here is to seek for service immediately. When driving with a derate, you can cause severe and permanent damage to your engine or emission system. You must be extremely cautious and careful when driving with an active derate! Locate the root of the issue as soon as possible and proceed with the resolution.

Maintenance Check Recommendations

Preventing a problem with the DPF system starts with basic maintenance. First of all, you can check for dirt on your fuel filter, in which case your engine will not be able to generate enough heat to regen itself or even allow you to initiate the active regeneration.

Sometimes your manufacturer or local service mechanic can require a valve adjustment as a part of the maintenance schedule. If you bypass or skip the valve adjustment when it is the recommended time, your engine performance can be negatively impacted, creating a preventing condition for the heat regeneration.

In most cases, the engine performance is compromised by the air filter if it is dirty. When dirty the air filter is restricting the amount of air that is required for the engine to reach top performance. Also, your injector, which is the PDF doser, is located in the exhaust right after your turbo, and it can become clogged and it is recommended to be cleaned periodically.

Another concern is the DPF system. You need to make sure that it is properly sealed. You can easily identify any leaks when you notice the black soot residue ner the sealing surfaces. Note that some manufacturers do not have a standard seal, and use exhaust tape instead. In that case, the tape has to be properly applied to prevent any leaking.

The maintenance guide provided in this article is not 100% necessary. It is more of a starter check to identify why your DPF system is not working correctly and why it will not begin a regeneration process.

The conclusion is that in case of an engine derate seeking a local service is necessary. It is extremely recommended to pay closer attention to your emission system when signs of upcoming derate are displayed.

We hope that this article was helpful and we wish you the best of luck!