How to Bypass the Def Level Sensor? – Detailed Guide

How to bypass DEF level sensor

Last updated on April 14th, 2023 at 04:00 pm

By-passing DEF level sensors are important to energy marketers since the sensors have to be replaced on a regular maintenance schedule. This software bypass is said to be a temporary fix until new sensors are made available in the market. 

DEF levels sensors are a new addition to some of the newer models of trucks. It works to ensure clean emissions of exhaust fumes from these trucks. To do this, the fluid levels should be filled regularly. An indicator light signals when the levels go low. A system bypass is required to prevent the shutting down of engines when the sensors fail. 

This article delves deeper into the DEF level sensors, explaining how they work, how to bypass them, and why there has been a shortage of the same.

How to Bypass the Def Level Sensor

How to bypass DEF level sensor

By-passing def level sensors have been permitted by the U.S. EPA as well as other engine manufacturers. They agree that the software bypass patch will serve to prevent the automatic shutting down of heavy-duty diesel due to faulty DEF fluid sensors.

The need for software bypass has been necessitated by the COVID-induced shortage of microchips that are needed to manufacture the DEF sensor replacements. These sensors are made to illuminate indicator lamps inside the cab at three intervals signaling low, empty, and empty and ignoring DEF levels. 

With the third warning light, the power in the engine is reduced to a maximum of 5 mph until the DEF levels are restored and the faulty sensor is replaced. The bypass is only made available to vehicle owners upon indication of the first of the three fault light indicator warnings before complete engine shutdown. 

What Are Def Sensors?

Diesel Engine Fluid DEF sensors are basically three sensors put in one apparatus—DEF level, temperature, and quality. For many tractors, they are also the source for derate messages.

The DEF sensors were the point used by the Environmental Protection Agency EPA to derate the truck with regards to after-treatment not working. The main components of an after-treatment system are the DEF injector, DEF tank assembly, and SCR catalyst. 

Why Are So Many Def Sensors Failing?

In the wake of the pandemic, many factories were shut down worldwide. These factories included those that produce urea, rubber, and DEF sensor chips. Since the truck’s sensors and chips are failing, there has been an increased demand for these components.

Following the increase in price and demand for urea worldwide, the price of DEF has skyrocketed. DEF quality sensors and chips keep failing rendering engines no longer operational. 

How Does the Def Level Sensor Work?

The DEF level sensor is a part of the DEF sending unit that works to measure the level of the fluid remaining in the DEF tank. In low levels, the DEF level sensor is that which sends a signal to the vehicle’s ECU which in turn triggers a warning light on the panel alerting the driver. 

Nowadays, the DEF comes standard in most of the newer trucks. It works in conjunction with the Selective Catalytic Reduction SCR system to break down the exhaust fumes of your truck and clean them a bit before they exit your exhaust system.

The catch with this system is that you need to keep the fluid reservoir filled regularly so it can function properly. 

What Happens if You Remove the Def Sensor?

Refilling DEF fluid levels not only takes time but also money. This explains why it has crossed the minds of many truck owners to delete the DEF system.

More often than not, DEFs, DPFs, and EGRs are required by law to be in all newer trucks that have these systems installed at the factory. If you reside in an area/state where the truck is required to pass the emissions tests, removing the DEF system can result in hefty fines.

Still, not all states have this emissions requirement. It is therefore advisable to stay in the loop on what is and what is not required in your state. 

Another consequence of removing the DEF sensor is that it might void the factory warranty on your truck. If anything goes wrong with your truck and you take it to the dealership for service, you might find that the warranty has been voided because of installing a diesel delete kit. 

Do You Have to Make an Appointment for a Def Sensor?

You can find the computer bypass at heavy-duty truck dealers and service centers. There are different types of heavy-duty diesel engines and the manufacturers are tasked to create software bypass for each one. Therefore, engine marketers are required to contact their dealer/service center to confirm the availability of the correct software patch for their vehicles. 

Once the supply of the DEF sensors is made available, truck owners will be contacted and be instructed to make a service appointment to replace the DEF sensor and restore the original engine calibration. 


DPFs are also diesel particulate filters, which are exhaust filters that are installed in-line on the exhaust system. They work to filter out particulates from the exhaust before it gets to leave the exhaust system and into the environment. 

The EPA requires that all diesel engine manufacturers include an integrated tiered warning system and/or gauges in the dash to alert drivers when the DEF tank level is running low. If the level drops below 10%, this should activate a warning light. At 5%, the lamp flashes, and at 2.5%, the light maintains a solid amber. In a case where the truck runs out of DEF, vehicle speed reduces to 5mph until you refill the tank.

The three major components of the SCR system are the DEF injector, SCR catalyst, and DEF tank assembly. 


DEF system serves an important role in the long run. Environmentally speaking, they ensure that trucks do not release harmful exhaust fumes into the environment.

However, they require regular maintenance and money. A system bypass is also necessary due to the recent rampant failure and shortage of DEF sensors. 

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