HOLLY, Mich., Nov. 18, 2025 (GLOBE NEWSWIRE) — Most drivers know the consequences of running out of fuel: The car or truck will stop running, and they’ll be stranded. But what many don’t realize is that if a diesel-powered vehicle runs out of diesel exhaust fluid (DEF), the result can be the same: They’re not going anywhere.
Modern diesel cars, trucks and SUVs have selective catalytic reduction (SCR) systems to reduce exhaust pollutants and meet emissions standards. These systems work by injecting diesel exhaust fluid (DEF), also known by the trademark AdBlue®, into exhaust to convert harmful nitrogen oxides (NOx) into nitrogen and water.
“Government regulations take emissions control very seriously,” explains Clay Parks, vice president of development for automotive chemical company Rislone. “SCR systems must be designed to warn drivers when DEF levels are getting low. Many vehicle manufacturers also program their vehicles to reduce performance when DEF levels drop below a certain threshold to encourage drivers to top it off. Fuel economy also suffers.”
In general, most drivers need to top off their DEF tanks every few thousand miles, but this will vary based on the size of the DEF tank, driving conditions and habits. Most newer vehicles have a DEF gauge right on the instrument cluster to make it easy to keep an eye on the fluid level.
The first sign that the DEF level is getting low is a warning light or notification that there are only a few hundred miles worth of DEF remaining in the tank. Ignoring the light or notification for too long can lead to the vehicle’s computer gradually cutting engine power and max speed (commonly referred to as “limp mode”) to nudge the driver to refill the DEF tank.
Once the DEF tank is empty, most vehicles will not restart or will only idle until DEF is added.
Aside from inconvenience, letting the DEF tank run dry repeatedly or for prolonged periods can damage the vehicle’s emissions and exhaust systems, leading to expensive repairs.
So, what should you do if your diesel runs out of DEF?
First, completely fill the tank with fresh DEF and add Rislone DEF Crystal Clean® Diesel DEF & SCR Emissions System Cleaner (p/n 4784) to dissolve any white crystal deposits that may have formed in the system when it was empty. These deposits can reduce engine power and increase fuel consumption.
Once the tank is full, the vehicle’s control module(s) and emissions control logic may need some time to reassess the state of the SCR system. That may require starting the engine and letting it idle or run under mild load, so the dosing pump, sensors, and related circuitry can get valid readings. It may take a while for the system to register the new fluid level and for the warning signals to clear. Some vehicles are programmed not to restart until the system has been reset by a dealer — so add “towing bill” to the list of reasons not to let the vehicle’s DEF level drop too low.
Learn more about protecting a diesel vehicle’s emissions system, avoiding costly repairs, and improving performance at Rislone.com/diesel-defense.
About Rislone
As a global leading engine treatment brand since 1921, Rislone has a long history of solving and preventing diesel engine issues. The company conducted years of research to develop solutions to help customers avoid expensive emissions system repair bills. All Rislone products are made in the USA and are available where auto parts are sold. Based in Holly, Michigan, Rislone is ISO 9001 certified.
AdBlue® is a registered trademark of VDA Verband der Automobilindustrie e.V.
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