No truck drivers love to see their engines going into derate mode, but it’s a necessary safety mechanism that triggers off when the engine conditions are not ideal. What can you do to restore complete engine functionality in this situation? Today, we will show you how to clear engine derate on a Peterbilt engine.

But before we get into the ‘’how-to’’ part, let’s discuss a bit more about engine derate. What factors spark it off? Can you do anything to prevent your engine from entering derate mode? What happens to your Peterbilt truck’s engine in derate mode? We will touch on all these queries to make you understand how you can maintain the engine better.

How To Clear Engine Derate Peterbilt: Causes And Solutions

Potential Cause	Fix
Excessive Exhaust Gas Temperature	Replace/fix the fuel injectors/ turbocharger. Clear up the restricted exhaust system. Tune the engine properly.
Excessive Coolant Temperature	Replace dirty coolant. Free up clogs in the radiator. Fix or replace the failing thermostat/ water pump.
Insufficient Fuel Pressure	Check for leaks in the fuel injectors. If you find any, fix them, or replace the fuel injectors altogether. Replace the fuel pump. Clear up or replace the fuel filters.

What Is Engine Derate?

Engine derate is an engine safety feature that restricts the performance of the engine. It springs into action when it becomes dangerous for the engine to operate at full capacity because of underlying faults and issues. When the engine goes into derate, an error code will pop up on the dashboard, indicating the root of the problem.

How To Clear Engine Derate Peterbilt: Step By Step

Step 1. Determine The Type Of Engine You Have

Not all Peterbilt engines are the same. Some Peterbilt trucks have PACCAR engines under their hoods, while Cummins engines power the rest. You will need to use engine-specific diagnostic tools to fix the problem. So, it’s important to know what engine you have. A simple Google search of your Peterbilt model should reveal the engine information.

Step 2. Get To The Root Of The Problem

Once you have figured out the engine model, it’s time to put your Sherlock Holmes cap on! You need to investigate and find out what went wrong that compelled your engine to put up its derate shield. Look at the error codes using the appropriate diagnostic software. You can also check the error code of your engine model online to discover the fault.

Deciphering the error codes will tell you what you need to do to fix the engine problem that has been leading your engine to derate. But you must also check engine parameters like fuel pressure, coolant temperature, etc., to rule out any undetected can of worms. If you notice any irregularities there, that might have been responsible for your engine to derate as well.

Of course, you must take a peek at the engine too. Some engine issues could be visible to the naked eye. Do you see any broken parts? Or cracks, perhaps? Is coolant or fuel leaking out of the engine compartment? These are obvious red flags that require immediate intervention. So, don’t forget to do a quick visual inspection.

Did everything check out? Turn your attention towards the sensors, then. A malfunctioning sensor could also make the engine derate. For example, a bad engine coolant temperature sensor could push the engine to derate mode as the coolant temperature goes beyond ideal limits without warning. So, make sure all sensors are working correctly.

Step 3. Clear The Error Codes

After you resolve the issues the error codes indicate, you need to clear the codes. You will find the ‘’clear’’ option on the diagnostic tool you used. However, do remember clearing the codes without sorting out the issues that had been causing them in the first place will not magically take your truck out of the derate mode.

To make sure that the codes have cleared for real, hook up the diagnostic tool again and run a scan. If the error codes reappear, it means the underlying issues persist, and the vehicle is likely to go into derate again soon. You must keep working on the truck till you get a scan result with no error codes.

Step 4. Make Sure That The Engine Is Running Right

You have cleared all the error codes, so that should be it, right? Most probably, your engine is fine now, but you never know! So, we strongly recommend checking it. First, connect a tachometer to the engine. The tachometer should have a red lead and a black lead. The black lead will go to the negative battery terminal of your truck.

The red lead will connect to the red wire on the ignition line. The red lead will send signals from the ignition coil to the tachometer. After the tachometer setup is complete, turn the key in the ignition and look at the reading on the tachometer. Consult the engine manual of your Peterbilt truck to find out the ideal RPM range.

For example, the default engine idle speed of a 2018 MX-11 engine in a Peterbilt truck is factory set to 650 RPM. You can program it to 700 RPM. If the RPM reading goes beyond 700, it indicates a serious problem. Faster than ideal RPM will overwork the engine and make it more vulnerable.

Other than RPM, you should also examine the engine temperature. Overheating is a pretty telling sign of an engine fault. The fluid levels should be part of any routine engine check. It’s no secret that low fluid levels can make the engine act crazy. So, check the fuel, coolant, and transmission fluid.

How To Reset Codes On A Peterbilt Engine?

Put the ignition key into the accessory position. Take a reset tool and connect it to the diagnostic port. Leave it on for a few minutes. Disconnect it after three to five minutes. Now, scan for error codes. If no more error codes pop up, everything is A-OK. If you still see error codes, you need to take the car to a service shop for a detailed inspection.

How Can You Avoid Engine Derate In A Peterbilt Truck?

There is no alternative to regular maintenance to keep your Peterbilt derate-free. You should change the oil regularly and replace dirty and worn-out filters. You should change the oil after every 25,000 miles of driving. Always keep an eye on the transmission fluid, coolant, and fuel levels. Make sure that they never drop below the minimum recommended levels.

Don’t go cheap on fuel. Make sure that it meets the octane number criteria set by the manufacturer. Monitor the sensors and ensure that they are functioning correctly. As mentioned earlier, faulty sensors can bring about a whole lot of trouble, including frequent engine derating.

Final Words

When your Peterbilt gets repeatedly stuck in derate mode, it points at severe underlying issues. Learning how to clear engine derate on Peterbilt is not futile without knowing how to mitigate the factors that keep pushing the engine to derate mode. So, you must maintain your Peterbilt properly and take care of any issue that might expose your truck’s engine to severe risk.

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Mark Williams

Founder and Author at Theautomobily

Mark Williams is the founder and author of Theautomobily located in Tucson, AZ. As a Mechanical Engineer,He has 15 years of experience in the automobile industry. Mark's deep understanding of various types of vehicles such as UTVs, ATVs, cars, Trucks, and lawnmowers which allows him to provide valuable insights and information.

How To Clear Engine Derate Peterbilt [Causes and Fixes]