How to Bypass Def System on Cummins? Where Is the Def Sensor Located?

how to bypass DEF system on Cummins

Last updated on July 6th, 2023 at 10:46 am

New Cummins engine models come with the DEF system. This helps to reduce the emission of harmful exhaust gases to the environment. However, there has been a shortage of the DEF sensors that has necessitated bypassing the system, so vehicles can go on their way. 

A software patch has been made available for vehicle owners with failing DEF sensors. This makes it possible to bypass the DEF system on Cummins and only works as a temporary fix until the shortage is eliminated. This is only possible if the owners qualify for the software patch. 

This article goes on to explain more about bypassing the DEF system on Cummins, how to clear the engine to derate, and how the DEF system works. 

How Do I Bypass the Def System on Cummins?

how to bypass DEF system on Cummins

A software bypass is available to many vehicles following the pandemic-induced shortage of DEF sensors. Cummins is no exception.

This software bypass remains to be a temporary fix-up until the new sensors are made available. Also, it is only available to vehicle owners once the DEF sensor fault light indicator signals the first of the three warnings before engine shutdown.  

How Do I Clear My Engine to Derate Cummins?

You may notice the engine codes 3713 and 3714 on your Cummins ISC engine. These codes are used to indicate a derated engine. It is possible to clear the codes by following the procedure below. 

To clear the engine to derate codes 3712 and 3714, the first step is to run the after-treatment maintenance command. This should be followed by running the NOx reset command. Then, perform a regen (that is recommended, not required). The codes will go inactive and are thus cleared. 

This procedure is applicable for OEM software, TEXA truck, or Cojali construction. 

Where Is the Def Sensor Located?

The EGR system installed in newer models of cars plays an important role. It is effective at reducing NOx emissions from engine combustion.

However, NOx emissions standards call for additional standards to further reduce the pollutant. Selective Catalytic Reduction (SCR) is tasked with this purpose. Its process usually starts with injecting the DEF into the exhaust system.

One of the system components is the DEF tank which houses the DEF controller, quality sensor, dosing unit, and fluid line. The DEF quality sensor is mounted on the side of the DEF tank. It works to detect the concentration of urea in the DEF and confirm whether it is acceptable for effective dosing. 

Why Do I Have to Bypass DEF Sensor?

You have a Bypass DEF Sensor because as these fluids are volatile and highly reactive, they can corrode the metal in your car’s exhaust, and there are other issues associated with it as well.

Take, for example, when DEF levels are running low, it becomes impossible to exceed the 5 MPH speed limit, not to mention the considerable expense involved in keeping the tanks replenished. Besides, the DEF system is notorious for recurring issues such as system failure, error codes, and diminished engine longevity.

Is Cummins Fresh Out of Def Sensors?

Despite the current shortage, not all DEF sensor manufacturers are ‘fresh out’ of DEF sensors. Cummins came through with the availability of a new software patch. 

Following the shortage of microchips, auto manufacturing has taken the hit and so have RVers. This has seen many RVers being stranded due to DEF sensor failures.

However, many manufacturers have been working to come up with a temporary fix, hence the software bypass. Cummins, EPA, and other industry types have followed up and suggested a software patch. Now, Cummins is using the temporary fix and issuing it to ‘eligible’ Cummins engine owners. 

Does the Cummins Have a Diesel Particulate Filter?

It was only until the 6.7L was the Cummins graced with a diesel particulate filter. This system works to prevent particulate matter from being routed into the atmosphere. This chamber is located downstream in the exhaust system and traps and stores soot.

Can I Get a Software Patch for My Cummins?

Now that Cummins only allows the software patch for ‘eligible’ Cummins engine owners, here’s how it works. 

Firstly, you have to qualify. Not all with a Cummins engine under their hoods will be able to get the software patch. Your vehicle must be disabled already in that the DEF system warning light displays on the dashboard. If it does not illuminate, you do not qualify. 

Another condition is that Cummins will not provide the software patch unless the DEF head in your rig is one that can be readily replaced due to the shortage. Vehicle owners are thus advised to inquire by sending an email including their serial numbers to Cummins.

The OEMs not currently participating can secure a DEF sensor replacement by reaching out to their vehicle manufacturer. If you are on the OK list, you can go ahead and schedule an appointment with the service facility.  


DEF can also go by urea, AdBlue, AUS 32, NOx reduction agent, and catalytic solution. 

The DEF tank is designed to hold 17 liters of DEF. This tank is to be refilled once the DEF level displays show that the DEF is low. The frequency of refilling DEF will depend on vehicle usage like driving conditions, speeds, loads, and trip distances. You can store DEF on sealed containers far from direct sunlight.

Moreover, DEF should not remain in the DEF tank of an unused vehicle for more than 6 months. You can test the DEF concentration using a refractometer that is calibrated for DEF. Water should never be added to DEF as it alters its concentration. 

Those who unfortunately fail to qualify for the DEF sensor replacement are pointed back to the alternative DEF sensor stimulator. If you manage to build one, keep it with you so when the warning light comes on, plug it in. This way, you can go merrily on your way until you get the software patch.  


Bypassing the DEF system seems to be the only working solution for the shortage of DEF sensors. It can get vehicles back on the road without worrying about derating of their engines. Cummins engine owners can check their eligibility for the software patch by sending an email to Cummins and then booking an appointment for installation.

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