What happens if you run out of DEF?

I recently got a diesel truck, and it’s my first time running low on diesel exhaust fluid (DEF). I’m still learning about proper truck care, but I’m just not sure what to do right now. What happens if my car runs out of DEF?

Kathryn Kurlychek · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
If you run out of DEF, you can usually get by with the simple fix of refilling the tank and restarting your vehicle. However, if you notice the DEF light appearing on your vehicle dashboard with unusual frequency, you may be looking at a bigger problem. 
In some cases, this can cause your exhaust system to clog with debris—which impacts your engine’s ability to run efficiently and can cause your vehicle to break down. 
DEF is a necessary component to the smooth operation of your diesel engine—so your truck won’t be able to run long without it. If you let your tank run dry, you may face serious consequences of hefty costs for repairs and replacement parts.
Keep in mind: DEF is a carefully regulated non-toxic substance with specific, chemical-purity requirements, so you should always buy pre-made DEF rather than attempting to make it yourself!
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