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What Happens When You Run Out of Diesel Exhaust Fluid?

No one loves the smell of diesel in the morning, and believe us—you don’t want to inhale its untreated exhaust, either. And the scent is nothing next to the evil emissions that diesel can unleash upon the atmosphere. That’s why there’s a system in place to stop them, and it all depends on an extremely talented liquid. But what happens when you run out of diesel exhaust fluid? Let’s put it this way: you won’t get very far.

Fair Warning

The Environmental Protection Agency requires that trucks made after 2010 use a diesel exhaust fluid, or DEF, which essentially purifies the emissions until they’re harmless. The EPA devised a way to ensure compliance, too. If your DEF runs dry, your truck nearly grinds to a halt.

Seriously? Yes. Your truck’s dashboard will give you plenty of warning when your DEF is getting too low. You’ll see an amber warning light go off if it dips below 10 percent. Then, as a gentle reminder, at 5 percent the light starts flashing. After that, the system tries to get your attention at 2.5 percent with a solid warning light. When the DEF runs out, the light turns red. It won’t step your rig from moving, but it will bust you down to 5 miles per hour, which is not an enjoyable experience on the highway.

How It Works

DEF is composed of 32.5 percent urea and 67.5 percent de-ionized water. It’s stored separately from the diesel in a tank with a blue filler cap. It’s non-hazardous, although it will stain your clothes. DEF is sprayed into the diesel’s exhaust stream. Inside the truck’s selective catalytic reduction catalyst, the DEF breaks down the harmful emissions into simple nitrogen, water vapor, and carbon dioxide.

Avoiding Trouble

We already know that you want to test the system for yourself, but the experiment is anticlimactic. You might get your truck home, but if there’s no DEF in the engine, it’s just not going to start. It will sit there stubbornly until you fill the tank back up to the top, and though it might run again, it won’t be happy.

HFI Truck Center can tell you more about what happens when you run out of diesel exhaust fluid. Better yet, we can show you an inventory of top-of-the-line vehicles that can keep you from finding out. We specialize in Isuzu truck service in Mountainside, New Jersey, and we’ve been in business since 1930. We can help keep you on the move.