Diesel Fluid Parts

What is a Diesel Exhaust Fluid Cap and where is it Located?

The diesel exhaust fluid cap lets you refill your diesel engine’s diesel exhaust fluid (DEF), also known as emissions fluid. Diesel exhaust fluid might sound like one of those mythical items like the shelf-stretcher or blinker fluid. Actually, though, in the past couple of years, diesel engine manufacturers have been using something called selective catalytic reduction (SCR) to reduce nitrous oxide (NOx) emissions. In the past, exhaust gas recirculation (EGR) was used to reduce NOx emissions. EGR effects combustion and makes the engine less fuel efficient. SCR reduces emissions in the catalytic converter, which gives engine manufacturers more leeway in tuning diesel engines, which means the engines can run better and use less fuel. 

The SCR system works by spraying DEF, a mixture of de-ionized water and urea into the catalytic converter. The DEF reacts with NOx to turn it into harmless water and nitrogen. The DEF gets sprayed out at about two to three percent the rate of fuel usage. The DEF is stored in a tank that you will need to refill about as often as you change your oil. 

To refill your DEF, you’ll have to twist off the DEF cap. In many trucks, the cap is found behind the fuel door, next to the fuel filler cap. In some cases, the DEF cap may be accessed under the hood or in the trunk. Some DEF caps can be locked with a key to prevent theft or tampering. Locking DEF caps will come from 1A Auto with the keys included. 

How do I Know if my DEF Cap Needs to be Replaced?

The DEF cap keeps fluid inside the tank and dirt and debris out. It can, over time, develop cracks and leaks. Dirt in the diesel exhaust fluid will eventually settle in the catalytic converter, making it less effective, which might cause you to fail an emissions inspection. Diesel exhaust fluid is not toxic, but it can corrode certain metals. So, it’s best not to let a leaking DEF cap go untreated. 

Can I Replace a Diesel Exhaust Fluid Cap Myself?

You can definitely change your own DEF cap. The DEF cap is placed to be easily accessible and is as easy to replace as a fuel filler cap. You’ll just have to twist off the old one, remove the strap that holds it in place, and then strap and twist on the new one. 

Need a Replacement Diesel Exhaust Fluid Filler Cap?

If your DEF cap has been damaged and needs to be replaced, you have come to the right place. 1A Auto carries a large selection of diesel exhaust fluid caps for many makes and models, and at great prices. Our replacements are just what you need to get your vehicle in good working order again.

At 1A Auto, we make shopping for a replacement diesel exhaust fluid (DEF) cap for your vehicle easy - we're here to help you select the right part! Call our customer service toll free at 888-844-3393 if you have any questions about our DEF tank covers, warranty, compatibility or to purchase, or you can buy online.