What is engine derate?

Engine derating is the modification of an engine to operate at a lower output than its normal capability. The reason for engine derating is to prolong its operating lifetime. The derating can be done willingly to avoid engine damages that may be due to substantial wear out.

In other words, you may derate your engine to operate under its highest rating power, rating of the current, or even below its voltage rating. For example, if you have a power generator, you can derate its engine to increase the engine lifespan, though, in one way, the power output is reduced than normal operation.

Engine derating is not done in only a power generator, but any machine using an engine can be derated. You can derate your vehicle’s engine also, but its speed will reduce.

In derating, this technique works to prevent the engine from overheating. Every engine is designed to work under specific conditions such as the ambient state. The engine derating is designed so that when the ambient temperature goes up than the normal operating state, the derating of the engine starts.

An engine designed to operate under temperatures of 30° C or 86° F, for example, the power may be reduced by 10% when the ambient temperatures rise to 40°C or 104° F. In this way, much heat is generated, and the engine performance goes down. Another effect resulting from increased engine heating is the high consumption of fuel.

Types of engine derating

As far as the engine derating is concerned, there are some ideas you need to know about the engine. One of the ideas is to understand the following three types of engine derating.

Intentional Derating

As pointed earlier, derating an engine aims to reduce its performance to prolong its lifespan. In intentional derating, the customer may ask the car’s manufacturer, to redesign or change the mode of the engine’s operation. The manufacturer then lowers the engine rating, and the performance will be operating under maximum capability.

In every car, the manufacturers’ mode of designing targets a specific purpose though this intention may differ with the customers’ desire. Therefore, the customer may request the car manufacturer to make some engine changes, such as derating.

There are so many reasons as to why the customer needs engine derating for their car. As the manufacturers know every engine configuration, they will reconfigure all defaults and insert new ones according to the customer’s desire.

Advantages of intentional engine derating

  • It is cost-saving in engine maintenance
  • Prolongs engines operating mode

Disadvantages of intentional engine derating

  • The speed performance is low

Unintentional Derate

Unintentional engine derating is the one that happens to the vessel without the owner knowing nor the manufacturer. This means the derating ca]n occur accidentally. Engines are designed to operate to do a specific work. Engine rating is specifically designed to last for a long time and present conducive services to the customer. When unplanned engine derating occurs, you may not notice and then continue operating your vessel. Since there is derating, the engine operations environment becomes altered, and it will start providing abnormal power supply. Eventually, the engine lifespan becomes short and may knockout or stop.

Advantages of unintentional engine derating

  • The lifespan of the engine is short.
  • High fuel consumption.
  • Low engine performance.
  • Costly in renewing a knocked engine.

5 MPH Engine Derating

5 MPH engine derating, is caused by different systems or sensors in the emission system. You have to understand if you encounter a 5 MPH engine derate, then the fixing is connected with emission. To understand the 5 MPH engine derating better, get to know the parts making up the emission system.

  • The DEF Doser Valve: its function is to regulate the DEF fluid injecting into the SCR Catalyst.
  • DEF Fluid tank: this is the tank holding the DEF fluid and has two sensors, level, and quality sensor. These sensors are responsible for ensuring a limited fluid concentration is allowed. If you get a derating, there is a probability of bad DEF fluid.
  • DEF Pump Assembly: its function is to pump DEF fluid. Derating can occur if the pump fails.
  • DEF Control Module: This system controls the entire emission system. 
  • NOx Sensors: it has two parts, an inlet sensor, and an outlet sensor. On the mode of how it operates, the sensors detect NOx exhausting, and if the exhaustion is high, it communicates to DEF/SCR. The DEF/SCR then injects urea to produce ammonia for emission regulation.
  • ECM: This part controls regeneration means and the DPF system for the emission system’s whole operation.

Advantages of 5 MPH engine derating

  • At the dealer level, the fault codes can be fixed through OTR Reset Tool and OTR Diagnostics. Therefore, you can replace the failed worn-out parts. Here, you will also get a chance to clear CEL.
  • OTR Reset Tool and OTR Diagnostics will be used in resetting 5MPH DEF derates. It is also advantageous as you won’t use your money or waste time going to shop for repair; OTRs will send the resets directly to the dealer.

Disadvantages of unintentional engine derating

  • Whenever there are emission failures, the DEF signal is low, just by one flash, and the driver may not notice.

How to fix engine derate

You may get tired of the engine derate in your car, and now you need to fix it and return your vessel to a normal operation; here some ways you can fix it. 

  • Repair the underlying problems and remove the fault codes that are responsible for derating. Fixing the underlying failures will help to clear derating codes permanently. 
  • Reset the counter at zero; this will help the engine to restart at full engine power.
  • Restart the engine three times for normal confirmation functionality.
  • If there is a failure in repair confirmation, then after 30 minutes, you will need to restart the engine as it will have derated.
  • After solving that problem, use an inducement counter to restart the engine and wait for about 30 minutes. The machine will resume normal operation if it detects no errors for that duration.

Can I drive with an engine derate?

Operating your car under engine derating may have some consequences. It is because serious permanent damage can happen to your engine or the emission system mode. The best way you have to ensure when you see that your engine is having derating, you have to seek immediate service.

If the derating has occurred while operating your car, you have to drive carefully and go to a repair shop as soon as possible.


Engine derating has some advantages and disadvantages. The prolonged running and low operating costs are some of the benefits. Consequently, there may happen that the engine operating under derating may have a shorter lifespan due to driving under abnormal conditions.

It is always advisable for the user to use their cars’ engines with no restricted engine efficiency conditions. 

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