What causes DEF head failure in an RV?

In this blog post, we will answer the question: “What causes DEF head failure in an RV?” We will talk about the DEF (Diesel Exhaust Fluid) head and the common problems. We will also talk about a few tips to recover from a DEF head failure. Furthermore, we will discuss the advantages of a DEF sensor simulator.

What causes DEF head failure in an RV?

A DEF head failure is caused if the engine fluid is routed in the wrong direction. The engine coolant in your RV is used to keep the DEF reservoir warm. When the coolant moves in the wrong direction, you will experience a DEF sensor failure. Once you experience a DEF head failure, it is important to take your vehicle to a professional to avoid major complications.

A DEF head failure is not something that you can predict. However, few measures can be taken into action after witnessing a DEF head failure. A DEF head failure can pop up at any time and it can happen to all types of RVs at one point in time. The chances of experiencing a DEF head are more common when your RV is parked idle for a long time.

Common DEF problems in RVs

DEF Problems are not something new and avoidable. These problems have been around for a long time. It is good to know about the common DEF problems to give you an idea and also help you run into a DEF head failure in the future. Below are some of the common DEF problems that cause a failure in RVs.

Dirt and metal contamination

  • Dirt and metal contamination is the most common DEF problem that can occur at any time. Contaminated DEF can also cause an abrasion of the DEF pump. This can happen if you re-use dirty DEF containers.
  • String DEF in carbon steel or copper containers can cause major issues. This can lead to rust and corrosion, which can later cause trouble for your vehicle.


  • Crystallization is another problem. These are mineral deposits that collect on the injector tips on the exhaust piping.
  • Injection of too much DEF can also lead to a DEF head failure. Overdosage of DEF might not fully hydrolyze and it gives room for crystallized deposits. This can also lead to DEF pump issues.
  • Filling up the DEF system with hard water can result in scale or deposits. While this can be a rare problem, the chances of it happening persists.

Urea Concentration

  • It is essential to have a proper mix of urea ratio to water. Excessive diluted DEF with water will not be strong enough to break down the NOx. This will prompt your engine to a fault code.
  • While most DEF is pre-mixed, it is still important to consider the ratio when it comes to topping up water. This can also affect the concentrations.

Using other fluids

  • Topping up the DEF tank with other fluids can cause problems. Fluids like engine oil, hydraulic oil, coolant, or diesel will be an issue. Since DEF is a water-based solution, it will mix with coolant but not with other fluids.

Cold weather

  • DEF has a freezing point of minus 11 degrees Celsius. Hence, the DEF must be melted for the exhaust system to function in cold climatic conditions.
  • The RV engine provides heat to melt the DEF with the coolant line. However, one common problem is with the thermostat. An electrical DEF tank heater can be a good solution.  

Those are some of the most common DEF problems that can take place in RVs. It’s always good to keep an eye out for these issues and try to maintain your RV as much as possible. All vehicles that were manufactured after 2010 are sure to have a DEF system. This is essential to run the vehicle better and it is also good for the environment.  

Tips to recover from a DEF head failure

Now that we know the common DEF problems, it is important to understand a few tips to recover from a DEF head failure. DEF head failures require attention immediately. At the most, your RV will give you a couple of hours to drive your vehicle. However, be sure to contact a professional mechanic as soon as you identify the problem.

Locate the DEF head

  • The first step is to locate the DEF head in your RV. Most RVs have the DEF head situated at the rear. Be sure to locate the DEF head since you will need to work on it. The DEF head is located at the top of the DEF tank.

Remove the cable

  • You will need to remove the cable that runs from the top of the DEF head. Be sure to remove the side that has the adaptor.

Plug in the simulator

  • You will need to plug in the simulator and you can zip tie it near the area. This will simulate the DEF head and should be back up and running after a couple of minutes.
  • Note that plugging in the simulator is just a temporary solution. You will need to get to a professional as soon as you can. The simulator can help you if you are stranded. Once you get to an expert, you will need to replace the DEF head or get it repaired.

Advantages of a DEF sensor simulator

  • A DEF sensor simulator is one of the best solutions to get your rig running even after a DEF head failure. There are many benefits of having a DEF sensor simulator. Here are some of the advantages described below.
  • To start, the DEF sensor simulator is not too expensive since it is made up of inexpensive material. Hence, you will not be spending much on this.
  • DEF sensor simulators assist as a temporary fix as soon as the DEF sensor failure occurs. You can easily drive your vehicle to a mechanic to safety with the help of a DEF sensor.
  • A DEF sensor simulator helps you drive your vehicle with full engine power and there is no need to compromise. Note that this is only a temporary fix.
  • Once you have the DEF sensor simulator installed, you can safely drive your RV until you find a mechanic.
  • You will need to replace the DEF head and make sure that you install a new one. The DEF head will last for years together without any issues.
  • Ultimately, it all depends on how you manage your RV. If you try to avoid the common problems that cause the DEF head to fail, you will prolong the life of the DEF head.
  • A DEF head plays a crucial part for RVs and it can lead to major trouble if you do not get it replaced at once.
  • Another easy tip is to simply replace the DEF head once in a couple of years. By doing this, you will not face any major issues.

DEF head failures are common and there is no need to panic when you encounter one. You can also pull over to a safe place and contact a mechanic to come to the rescue. If you are not aware of working with DEF head sensors, do not try to make any alterations on your own. You can also carry a spare DEF head along with you.

By understanding the causes of the DEF head failure and identifying the common problems, you can easily prevent this from happening. Make sure not to use dirty DEF containers, this can be a major cause for the DEF head to fail. At the same time, have a proper mix ratio of Urea with water to avoid further problems.


In this blog post, we have answered the question: “What causes DEF head failure in an RV?” We have talked about the DEF (Diesel Exhaust Fluid) head and the common problems. We have also talked about a few tips to recover from a DEF head failure. Furthermore, we have discussed the advantages of a DEF sensor simulator.



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