What Happens If You Don’t Put DEF in Your Diesel Truck?

DEF reduces the number of harmful chemicals emitted by your vehicle.

Diesel vehicle manufacturers are required by the EPA to make it harder for the vehicle to start if the exhaust fluid runs out so that the owner of the vehicle takes the issue seriously.

DEF System

Is It Possible For a Diesel Truck To Run Without DEF Fluid?

In some trucks with low levels of DEF fluid, the trucks ran sluggish and would not go faster than 5 mph.

If the vehicle runs out of fluid, it will not start, or its speed will not exceed 5 mph. There is a red warning light on the dashboard screen if the fluid is not replaced.

There is a system on the dashboard display that will alert the driver when the Diesel Exhaust Fluid tank level falls below 10%.

An amber warning light will come on the dashboard display when the DEF level is less than ten percent.

When it falls below 5%, the light begins to flash, and when it drops below 2.5%, it becomes brighter.

What Is DEF?

The diesel exhaust fluid has a mixture of Urea and deionized water, which is non-toxic.

Reducing the harmful NOx emission gasses in diesel-powered vehicles that are present in the exhaust gasses into nitrogen and water that are harmless to the environment is its primary function.

How Much DEF Will A Truck Consume?

Depending on the truck, the amount of DEF consumed varies. The diesel exhaust fluid consumption can be measured as a ratio of your vehicle’s miles traveled.

A ratio like this is referred to as a treating rate. The treatment rate for medium and heavy-duty trucks is usually between 2 and 3 percent.

If your vehicle has a fuel economy of 8 miles per gallon and a treat rate of 2%, your vehicle will use one gallon of diesel exhaust fluid every 400 miles.

The treatment rate isn’t always higher than the manufacturers’ specifications.

How Does DEF Work?

Nitrogen oxides, carbon monoxide, Sulfur dioxide, and soot are some of the harmful gasses that can be found when exhaust gasses leave the combustion chamber.

Any soot or ash that may be present is removed from the exhaust gasses through the particulate filter.

Exhaust gasses flow past a nozzle that continuously sprays diesel exhaust fluid after the particulate filter. Deionized water and pure Urea are contained in this fluid.

There is a mixture of diesel exhaust fluid and hot exhaust gasses.

In the presence of catalysts and several metal compounds, the diesel exhaust fluid and the hot exhaust gasses can be used to reduce nitrogen di-oxides and monoxides.

The SCR system is combined with an exhaust gas recirculation system in most cars.

Part of the exhaust gasses can be returned to the chamber to complete the burning of unburnt gasses.

Does DEF Freeze The Tank?

There is a possibility of diesel exhaust fluid freezing in cold weather. The diesel exhaust fluid can freeze at 120 F and then evaporate at temperatures above 860 F.

Many trucks have heating elements in their tanks that can be used to de-freeze the fluid tank.

When the engine stops, the DEF feeders and supply tubes are emptied because they are heated to prevent them from freezing.

This process is done to prevent the tubes from freezing. Most vehicle manufacturers have a solution to the problem of diesel exhaust fluid freezing.


What Happens When DEF Is filled With Diesel?

If your vehicle smells like gas, it is probably not related to the DEF. It is difficult to distinguish diesel exhaust fluid tubes and diesel filler necks.

There are nozzles for diesel and exhaust fluid. The DEF nozzle is 0.75 inches and the Diesel Nozzle is 0.87 inches.

If you accidentally fill the DEF tank with diesel, it will float on top of the Diesel Exhaust Fluid and cause your engine to not start.

If this happens, you should take your vehicle to the service center for repairs.

DEF Substitutes

Diesel exhaust fluid is made up of a chemical disposition of deionized water and urea that is derived from urine but is synthetically made.

AdBlue is a blue color due to the mix of urea and deionized water used for diesel exhaust fluid.

DEF can cause serious damage to your diesel or other areas of your engine if it is mixed with your exhaust fluid.

If you’re stuck without a substitute, people recommend using a windshield washer with ammonia to perform the same task, but it’s best to use a proper diesel exhaust fluid to maintain the proper working order and health of your diesel engine.

Many people think that urine can be used as a substitute for DEF to save money, but the concentration levels needed are not the right levels of purity and therefore you should not use urine as a DEF substitute.

If you want to avoid getting stuck without DEF in your diesel vehicle, you should make a habit of topping up your fluid whenever you get diesel for your vehicle as this will keep your car or truck running smoothly.

How Long Will DEF Last?

A full tank of diesel exhaust fluid should last around 6300 miles but this can vary from vehicle to vehicle, and if your sensor is faulty this can be a massive headache.

The temperature, level, and quality of your fluid can be measured by this part and can cost over a thousand dollars for a replacement.

If your vehicle is not starting because of low fluid levels or empty fluid levels, then you should have your sensor checked.

DEF with high water content can freeze easily in colder temperatures, so make sure you store it correctly.

Even if it had been left sitting for a long time, the ingredients remain mixed in the solution and it doesn’t require any mixing before use as it doesn’t degrade or break down over time.

DEF System


Diesel exhaust fluid or AdBlue is an essential part of diesel vehicles as it reduces air pollutants and emissions making it legal for road use.

Unless you want to be stuck with a vehicle that refuses to start, don’t try to find out what happens if you run out of DEF.

Topping up your diesel exhaust fluid levels every time you refill your tank is the best way to make sure you are never left short, although there will be warnings in place to let you know if you start running low.

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