Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. Is It Safe to Drive With the DEF Light On?

Is It Safe to Drive With the DEF Light On?

DEF Light

A tractor trailer at the side of the road ideally means that the driver has pulled over for a well-earned nap. Of course it could also mean a breakdown. One troubling scenario to have is having the DEF light come on.

The DEF (diesel exhaust fluid) light is a driver warning system that lets you know when your DEF tank is nearly empty. This affects truck drivers more than it does drivers of passenger vehicles. DEF is, essentially, a mixture that is added to the vehicle's engine to reduce environmental harm by combining with the diesel gas. The DEF light glows when it is time to add fluid, and as to whether it is safe to drive with the light on, yes, it is. But you shouldn’t. If you do, you could be in trouble.

Here’s are some things to know about driving with a DEF light on:

  • Before your DEF tank ends up empty, you will see an alert on your dash in the form of the DEF light. If your DEF drops below 2.5%, the light will be a solid amber. If you decide to ignore it, at the point where you run out of DEF, the light will glow solid red.

  • It gets worse. If you ignore the solid red, your vehicle speed will be reduced to a snail’s pace – 5 miles per hour – until you top up the DEF tank.

  • The DEF warning light can also indicate contaminated fuel. The effect will be the same. This type of contamination most often occurs when someone accidentally puts diesel fuel in the DEF tank.

Most often, loss of DEF fluid is due to driver error. Drivers sometimes forget to check the DEF fluid when they check their fuel levels. This not only results in a loss of power, it can also damage the DEF system itself. The repairs can be very costly, and of course can result in unwanted downtime for the driver.

The solution, obviously, is proactive maintenance. Drivers need to be vigilant when it comes to DEF, so that they don’t lose time, damage their vehicles, and end up in big trouble with their employer. Ignoring the DEF light is never a good idea, so if it comes on, the driver should pull over and have their DEF refilled immediately.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
Auto Safety Tips
Driving is more than a way to get from point A to point B. Owning and driving a car can also be a highly enjoyable experience. Whether a person is driving...
P0291OBD-II Trouble Code: Cylinder 11 Injector Circuit Low
P0291 code definition When your vehicle’s PCM registers the P0291 code, it means that a voltage reading came from the fuel injector circuit – for cylinder number 11’s fuel injector –...

Related questions

Q: Is it safe to drive with bushings gone?

Hi there. To be blunt, no, it's not safe to drive a vehicle that have any bushings that are completely broken. Bushings are designed to cushion critical steering or front end components. When they fail, those components can snap and...

Q: How do I turn on the hazard lights in a 2012 Dodge Ram?

In the event of an emergency, you should always turn on your hazard lights. Your hazard light switch is placed in the instrument panel; press the button once to turn on your hazard lights, and a second time to turn...

Q: Gas pedal does not respond very quickly, cruise control acts up too

What you are describing sounds to me like the transmission is not down shifting correctly instead of the engine causing the hesitation. I have found two recalls that may fix your problem. The first calls for the engine/transmission module to...