Warning Sorry, you're using a web browser that is no longer supported. For the best experience please upgrade or visit the site on another browser.
Skip to content
15% OFF $75+ using code: DEC15 Online, Ship to Home Only. See Details

What Is Diesel Exhaust Fluid?

Diesel exhaust fluid, or DEF, is a solution used in diesel engines to help manage emissions. When diesel exhaust fluid runs out, it causes a dramatic reduction in power or completely shuts down the engine. A diesel vehicle will be equipped with a specific reservoir for DEF, and it’s likely these vehicles will have a dash light indicating when DEF is low. Find a full selection of diesel exhaust fluid at O’Reilly Auto Parts.
Show More Show Less
O'Reilly Diesel Exhaust Fluid

O’Reilly Chemicals 2.5 Gallon Diesel Exhaust Fluid
Peak Blue DEF Diesel Exhaust Fluid

Peak BlueDEF 2.5 Gallon Diesel Exhaust Fluid

Why Do I Need Diesel Exhaust Fluid?

Diesel engines create emissions that can potentially create permanent environmental damage. By adding diesel exhaust fluid to these engines, their emissions are neutralized to nitrogen and water, which are harmless to the environment.
Show More Show Less

Additional Diesel Resources

Testing Diesel Glow Plugs

How To: Test Glow Plugs
Diesel fuel under high pressure at high temperatures self-combusts, and in cold weather, glow plugs assist this process by heating the combustion chamber for cold starts.
Changing a diesel fuel filter

How To: Change Diesel Fuel Filters
Diesel fuel filters get dirty and require changing, just like any filter. Your vehicle’s manufacturer will specify how often they need to be changed, but consider changing them before each winter.

You Might Also Need

Gloves Gloves
Funnel Funnel
Shop Towels Shop Towels

The automotive repair work depicted in this series is performed under the direction of the manufacturer of the product featured. Prior to undertaking any of the demonstrated repairs on your vehicle, we suggest you consult with a certified mechanic or another professional who can adequately advise you of the proper repair or remedy required. O’Reilly Automotive Stores, Inc. and its affiliates (“O’Reilly”) disclaims any responsibility for injury or damage resulting from a viewer’s attempt to recreate the repairs shown in this series.