Nowadays, cars are getting more and more complicated. Before, you only had to worry about having sufficient oil, gas, and water in your car. This list gets even longer with today’s requirements, including the DEF. But what most people are concerned with is how long you can drive with DEF light on.
On that note, how far can you drive with the DEF light on? Once the DEF light comes on, you only have about 50 to 100 miles to drive. This depends on your vehicle and the size of the DEF tank. If you continue driving beyond the 100-mile mark, you risk your vehicle getting into limp mode, where the engine limits the speed to prevent further damage.
Check out the information below to understand more about the driving distance when the light comes on and the best speed to drive. I have also gone deeper to explain how to avoid it and much more.
How Far Can You Drive with the DEF Light On?
What is DEF fluid first of all? Diesel Exhaust Fluid (DEF), a mixture of urea and deionized water, helps convert nitrogen oxides (NOx) into harmless nitrogen and water in diesel engines. DEF is essential for diesel vehicles to comply with federal emissions standards, and it’s just as important as fuel, coolant, and oil.
Can you drive with Driving with the DEF light on? Yes, it is possible, but you will not go very far. Usually, when the light comes on, it is accompanied by the warning message “5mph Max Speed in 100 mi, Service DEF System, See Dealer.”
So, how far can you drive with DEF light on? You have just about 100 miles to refill your DEF—failure to do so and your vehicle goes into limp mode. This is its defense measure, where the engine limits the speed to prevent damage.
Is It Safe to Drive with DEF Light On?
Initially, it may seem safe to drive with the Diesel Exhaust Fluid light on, but no, it is not safe to drive with the DEF (Diesel Exhaust Fluid) light blinking. It could lead to reduced engine power or even engine failure if ignored; you should get your vehicle checked by a mechanic as soon as possible.
Why you shouldn’t drive with a blinking DEF light:
- Low DEF level: A blinking DEF light usually means the DEF fluid level is dangerously low, and driving further could cause the system to malfunction.
- System malfunction: A blinking light could also indicate a problem with the DEF system itself, like a faulty sensor or injector.
- Engine derating: In many vehicles, a low DEF level can trigger engine power reduction to protect the emissions system, making driving difficult.
What Should You Do If Your DEF Light is Blinking?
- Refill DEF: First, check your DEF fluid level and refill it if necessary.
- Get it checked: Even if you refill the DEF, it’s important to have your vehicle inspected by a mechanic to diagnose the reason for the blinking light and address any underlying issues.
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How Often Should I Fill the DEF Tank?
This depends on your engine type, the usage of your truck, the MPG you drive at, and the DEF tank size. For example, if your vehicle is a ¾ ton pickup equipped with a 6.7L engine running lightly, you may only need to top up the DEF tank every 8000 miles. On average, light-duty trucks tend to consume approximately 2 to 3 gallons of DEF for every 800 miles. A diesel truck with 20+ mpg can go 8000 to 10,000 miles on 10 gallons of DEF.
How Do I Prevent the DEF Light from Coming On?
The simple and short answer to this is to refill the DEF tank regularly. This way, you will not have to worry about the DEF warning light coming on or suffering the consequences of the same. Hence, inspecting the DEF levels and regularly refilling them when necessary is advisable. While at it, ensure that you carefully review the owner’s manual for instructions on locating the DEF filler port to avoid contaminating your fuel.
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Frequently Asked Questions (FAQs)
What are the Consequences of Not Filling Out DEF in Time?
Low DEF levels directly impact the engine performance, prompting the car’s engine to activate the limp mode. This means you cannot drive your car until you refill the DEF efficiently. Moreover, it is likely to cause the car to break down due to the reduced engine performance. There are also chances of reduced fuel economy and increased emission production.
Why is My DEF Light On, But the Tank is Full?
DEF light blinking when the tank is full is a sign of trouble with the level sensor. You must check the float as it could be stuck at one spot while the fluid moves. This is what may have brought about this error. If that is the case, slightly shake it loose or re-install it to deactivate the light. You can also inspect the DEF pump.
Conclusion
If your DEF light comes on, you cannot go very far, only about 100 miles. Hence, refilling is advisable as soon as the warning light appears. This will spare you a lot of other issues, such as increased dangerous emissions, a clogged exhaust system, or the engine shutting off completely.
