How Far Can You Drive with the DEF Light On

It’s a familiar situation – you’re cruising down the highway when suddenly the DEF (Diesel Exhaust Fluid) light comes on. Fear not! This comprehensive guide will help you understand what the DEF light is all about, how far can you drive with the def light on, and what to do when it happens. Let’s dive in!

How Far Can You Drive with DEF Light On

The answer to how far can you drive with the def light on varies depending on the make and model of your vehicle, as well as its DEF system. Generally speaking, you can drive anywhere between 50 to 200 miles before experiencing reduced performance. However, the exact distance will be indicated in your vehicle’s owner’s manual.

Understanding the DEF Light

The DEF light illuminates when your vehicle’s diesel exhaust fluid level is low or there’s an issue with the system. DEF is a crucial component in reducing harmful nitrogen oxide emissions from diesel engines.

The Importance of DEF

The use of DEF is crucial for maintaining your vehicle’s performance and abiding by environmental regulations. Running your engine with a low DEF level can result in decreased fuel efficiency, a derated engine, or even damage to the SCR (Selective Catalytic Reduction) system.

Identifying DEF Warning Stages

Your vehicle’s DEF system typically has two to three warning stages, which are:

First Warning: Low DEF Level

When the DEF light comes on, it usually means that the fluid level is low. At this stage, you should refill the DEF tank as soon as possible to avoid potential complications.

Second Warning: Severe DEF Level

If you ignore the first warning, the DEF light will flash, signaling a more severe issue. At this point, your vehicle’s performance may become compromised, and you might notice a decrease in power.

Third Warning: Engine Derate

In some cases, a third warning might occur – the engine derates, significantly reducing power to prevent further damage. In this scenario, you should immediately address the DEF issue before driving further.

When to Refill Your DEF Tank

The Golden Rule

The golden rule when it comes to DEF is never to let the tank run dry. By ensuring your tank is always adequately filled, you can avoid potential damage and costly repairs.

Regular Maintenance

Incorporate DEF checks into your vehicle’s regular maintenance schedule. This proactive approach will help to catch any potential issues early on.

You Can See:

Troubleshooting DEF Light Issues

If your DEF light stays on even after refilling the tank, here are some common problems to investigate:

DEF Contamination

Contaminated DEF can trigger the DEF light. Drain and clean the DEF tank before refilling it with fresh fluid to address this issue.

Damaged DEF Pump

A faulty DEF pump could also cause the DEF light to stay on. Have a professional mechanic inspect the pump for any signs of damage.

Clogged DEF Injector

A clogged injector may restrict DEF flow, which could also trigger the light. Inspect the injector and clean it if necessary.

How Far Can You Drive with the DEF Light On


How far can you drive with the def light on?

The distance varies depending on your vehicle’s make and model, but it usually ranges between 50 to 200 miles. Check your owner’s manual for the exact number.

Can you damage your engine by driving with the DEF light on?

Yes, driving with the DEF light on can result in decreased fuel efficiency, a derated engine, and potentially damage to the SCR system. It’s essential to address the issue as soon as possible to avoid costly repairs.

Can you reset the DEF light yourself?

In some cases, the DEF light may reset itself after you’ve refilled the tank. If it doesn’t, you may need to have a mechanic reset it using specialized diagnostic tools.

Is it illegal to drive with the DEF light on?

While it may not be explicitly illegal, driving with the DEF light on means that your vehicle isn’t meeting environmental regulations. You could face penalties for non-compliance if caught by authorities.

How often should you refill your DEF tank?

The frequency of refilling your DEF tank depends on your driving habits and vehicle model. As a rule of thumb, it’s a good idea to check the DEF level during regular maintenance intervals.

What are the signs of a bad DEF pump?

A bad DEF pump may result in the DEF light staying on, decreased engine performance, or warning messages on the dashboard. If you suspect a faulty pump, have a mechanic inspect it immediately.

Know Why DEF Light Blinking On Freightliner Tank Is Full?


Understanding how far can you drive with the def light on is crucial for maintaining your vehicle’s performance and adhering to environmental regulations. Remember to never let the DEF tank run dry, and address any DEF light issues promptly. By staying proactive with vehicle maintenance and troubleshooting, you can keep your diesel engine running smoothly and efficiently.

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