Why RVers Should Know What a DEF Head Is

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A car being filled up their DEF heads with DEF fluid at a gas station

While the term DEF heads may sound like fans of some new music style, that’s not exactly what we’re talking about today.

Starting in 2010, they became an important component in many newer RVs and trucks. So why should RVers know what a DEF head is? Let’s find out.

What Is a DEF Head?

A DEF head monitors the entire Diesel Exhaust Fluid system. It communicates to the essential components the quality and quantity of DEF in the system and that everything runs as it should.

It gives the engine control module the green light to start the engine. If a vehicle’s DEF head isn’t working, it will not run correctly.

A DEF heads cap on a car

What Types of Vehicles Have DEF Heads?

In 2010, the Environmental Protection Agency required all medium and heavy-duty vehicles with diesel engines to begin using a DEF system to reduce emissions.

Passenger vehicles, big 18-wheelers, and motorhomes made after 2010 with diesel engines will have DEF tanks that drivers need to keep filled with diesel exhaust fluid.

Some drivers opt for older vehicles or gas engines to avoid dealing with complex DEF systems.

Are DEF Head Failures Common?

Sadly, DEF head failures have become increasingly common, especially since 2017.

The EPA made a major adjustment to measure the concentration of the DEF to ensure drivers weren’t diluting the fluid with water.

This adjustment resulted in sensor failures occurring at an alarming rate, especially among motorhomes. 

These DEF head failures were complicated because they occurred randomly on many units, and parts have been hard to get. Many RVers found themselves stranded thousands of miles from home and unable to do anything about it. 

Why Are DEF Sensors Failing?

While the DEF sensors initially seemed to fail for no reason, it was later determined it was a heat issue. The sensors used an electronic circuit board that would fail due to exposure to tremendous heat from the engine’s exhaust system.

These systems constantly circulated hot engine coolant through the DEF head. It’s no secret that heat and electronics typically don’t agree with each other.

Excessive heat led to a drastically reduced sensor life expectancy, which meant they would fail out of nowhere.

Are DEF System Repairs Expensive?

Most DEF head system repairs are going to cost you more than $1,000. However, once a DEF system reaches more than 200,000 miles, it’s recommended that drivers replace the entire system.

This can cost upwards of $10,000 to replace. Few drivers will likely want to dump $10,000 on a vehicle with 200,000 miles. However, many drivers might not have many options.

Tips to Protect Your DEF System

You want to take good care of your vehicle’s DEF system.

Here are some tips for protecting it so you don’t face a major issue and expensive repair.

Let’s get started.

Don’t Confuse Filling Ports

The location of DEF head filling ports will vary based on the vehicle. Some manufacturers place them next to the diesel fill port, and others put them under the hood.

However, no matter the location of your filling ports, you need to give your full attention to the task at hand when dumping DEF or any other fluids into your system.

You can make a huge and costly mistake by dumping the wrong fluid into the wrong tank. Putting DEF in your diesel tank can be an extremely expensive mistake.

Doing so may cause your engine to fail to start, rust your tank, and damage the system. So pay attention when filling your tank, and ensure you put the correct fluids in the proper filling ports.

A DEF heads station at a gas station

Buy High-Quality DEF

Never buy low-quality diesel exhaust fluid. The stakes are far too high for your diesel engine.

You may save money sometimes, but getting a bad batch of DEF will easily eat away at any savings you have experienced. Remember, DEF system repairs are never cheap. 

Pro Tip: Avoid buying your DEF fluid from Walmart! Here are 5 Reasons to not purchase Walmart DEF Fluid

Don’t Buy too Much DEF

If your vehicle uses a DEF head, have some fluid on hand. However, avoid buying so much that it just sits in the box waiting to get used.

The best-by date on DEF is typically one year from the manufactured date. Don’t dump expired DEF into your vehicle’s system. It can cost a host of expensive damage that you want to avoid.

A person filling up their DEF heads with DEF fluid

Use Sealed Containers to Store DEF

Some diesel drivers have purchased DEF and discovered someone tampered with the seal under the cap. It takes a very “special” person to deliberately break the seal or tamper with DEF on store shelves.

You could end up dumping contaminated fluids into your system if you don’t catch the mistake. If someone were to have contaminated the DEF, you could soon end up with a costly repair bill.

Can You Bypass a DEF System?

Some diesel owners will pay several thousand dollars to “delete” the DEF emissions system on their diesel vehicles.

They typically notice increased MPGs and avoid many of the costly repairs associated with them. Sadly, tampering with the emission system on your car is illegal in all 50 states.

If you live in a state with no emissions testing, you may not get caught, but you’ll void your warranty and reduce the chances of trading the vehicle with a dealer.

A “deleted” vehicle will not pass emissions testing in any states or areas that require it to register a vehicle. We would never encourage you or anyone else to break local, state, or federal laws.

Keep in Mind: Have you ever had to deal with the smell of Diesel on your clothes? Here are a few ways to Get Diesel Smell Out of your clothing!

Don’t Let a DEF Head Disaster Ruin Your RV Adventures

Luckily, technologies have improved for DEF heads, and the newer models haven’t experienced the same issues.

Some RVers will travel with a DEF emulator that can help them get to a mechanic or shop to address the issue.

These emulators send the necessary information to the system for the vehicle to function normally. It’s a temporary fix to avoid letting a DEF head ruin your RV adventure!

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