How to Reset DEF Light On Mercedes Sprinter

Are you thinking about how to reset the DEF light on your Mercedes Sprinter? Worry no more! We researched the steps and simplified them for you.

To reset the DEF light, follow these steps:

  1. Turn the ignition on.
  2. Press and hold the "0" button until you hear a beep sound.
  3. Press the "M" button until the screen displays "Reset 51."
  4. Press and hold the "0" button until the screen says that the reset is done.
  5. Turn the key on.

This article discusses the DEF light, its importance, and how the DEF improves driving. We'll also give you helpful information about the DEF. You can learn so much more with us. So, continue reading!

Many different car dashboard lights - How to Reset Def Light On Mercedes Sprinter

How to Reset DEF Light on Mercedes Sprinter

Resetting the DEF light is essential to monitor the car's performance when driving. Here are the steps to reset the DEF light properly.

Start the Ignition

Starting the ignition helps the engine heat up. Ignition will help the DEF light illuminate when you reset it.

Press and Hold the "0" Button

There are two buttons located at the left of the dashboard labeled "M" and "0." You should press the "0" button and hold it until you hear a beep sound.

Press the "M" Button

Press the "M" button once to see the "Reset 51" display on the screen. The "Reset 51" is a term for restarting the DEF light.

Press and Hold the "0" Button

You should press and hold the "0" button to finish resetting. The screen should say that it's done.

Turn the Key On

Lastly, you should turn the key on and start driving to test the DEF light.

What are DEF and DEF Light?

Low fuel warning light

DEF is a non-hazardous solution mainly composed of urea and deionized water, short for diesel engine fluid. The DEF improves the engine performance and is meant to reduce the harm of gas emissions.

The chemical composition of the DEF will then be converted into ammonia and carbon dioxide, resulting in safer air emissions.

A gas guage in a car reads empty and shows the warning light to let the driver know they are out of gas and need to refuel.

On the other hand, the DEF light indicates the fluid level of the exhaust system. It automatically changes color depending on the DEF level.

Also, the DEF light helps you prepare for inconveniences like engine malfunctions before driving. It gives you a warning so that you can estimate how far you can drive.

Meaning of DEF Light Colors

Modern car dashboard with error signs close up side view

The colors of the DEF light differ in what they are trying to tell you. Specifically, if the amount of DEF is enough. See below the DEF light colors and what they mean.


This is the safest color of DEF light. This means that the DEF level is still enough for some features to function. Each function has a unique icon or shape. Refer to the user's manual to see what these icons mean.


Once you've used a lot of DEF, the indicator will light the icons orange to show that the DEF level is low. Due to this, the driving speed will be reduced to 25 miles per hour.


A red light means the DEF tank is empty. The driving speed will be reduced to three miles per hour. The engine will stop working after a few minutes. You need to refill the DEF tank to continue driving.

DEF Light Isn't Turning On

Many different car dashboard lights in closeup

If the DEF light is not glowing, there might be a problem with the wiring under the dashboard. See if the DEF light is the only icon that's not glowing or if all other icons do not emit light.

You may try refilling the DEF tank to see if the DEF light will work. Otherwise, you should ask a professional to check if the wires are correctly connected under the dashboard.

The DEF light is significant to prevent you from guessing if the DEF tank is full or empty.

When to Reset DEF Light?

Man hand touching the LCD screen in the car. Using navigation system on dashboard of modern car

Resetting the DEF light also means refilling the DEF tank. The tank can signal the dashboard once the amount is enough for driving.

However, you may drain the DEF tank and clean it thoroughly. Sometimes, the dashboard displays an error due to uncleaned tanks and containers.

We'll talk about cleaning the DEF tank later in this article.

How Much DEF Do You Need?

Oil Changing

The Mercedes Sprinter can hold up to 6.6 gallons of DEF, while other ordinary cars can hold 5-7 gallons of DEF, depending on the manufacturer.

You can operate a car with at least a gallon of DEF, but we do not recommend refilling the DEF tank with too little. Otherwise, the engine may suffer damage too early.

How to Refill the DEF?

Hand a man open the Engine oil cap in engine room for check and Adding engine oil to engine car

Depending on fuel consumption, you can refill the DEF tank in full every 3-4 times you fill the fuel tank. This is to ensure that the engine will emit environmentally friendly gas.

See this DEF on Amazon.

To refill the DEF, follow these steps:

  1. Remove the key from the ignition, then wear your gloves and mask.
  2. Pull the hood release clutch at the left of the brake.
  3. Close all the doors and windows so that ammonia cannot evaporate inside the car.
  4. Open the hood and remove the DEF cap.
  5. Fill in the DEF until the tank is full. Put back the DEF cap and close the car's hood.

Is DEF Different From Fuel?

Refuelling the car at a gas station fuel pump. Man driver hand refilling and pumping gasoline oil the car with fuel at he refuel station. Car refuelling on petrol station. Fuel pump at station

The DEF has a separate tank from the fuel tank. Fuel is what activates the combustion system to make the engine operate. On the other hand, DEF cleans the engine to minimize harmful chemicals by exhausting the air contaminants.

If you're wondering why you cannot use DEF as a fuel, it's simply because the two have different chemical components in which changing one ingredient can affect the engine's performance.

DEF is Accidentally Filled Into the Fuel Tank

Driver is spreading his hands on a car gas tank with a funnel background.

Once you've accidentally filled DEF into the fuel tank, immediately drain the fuel tank. The engine may not work correctly once it detects an unusual fluid, like DEF. To drain the DEF out of the fuel tank, follow these steps:

  1. Find the best spot for draining.
  2. Locate the fuel tank filter under the air filter cartridge, then remove the clips with a pair of pliers.
  3. Remove the engine cover with a screwdriver. The air will then force the DEF to drip. We do not recommend reusing this DEF as the fuel has mixed with it already.
  4. When the draining is done, put back all the covers.
  5. Test the air filter by turning on the key without turning on the engine. Wait for at least 30 seconds before you turn the ignition on.

After draining the DEF from the fuel tank, you can refill the fuel to let you drive the car. If you have more time, you may also remove the fuel tank to clean it.

The reason why cleaning is not initially suggested is that cleaning the fuel tank requires more time and effort compared to draining. You also need hot water and a cleaning solution, which are not readily available.

Auto Mechanic Series

Follow these steps to remove the fuel tank:

  1. Wear a mask and gloves.
  2. Turn off the engine and detach the cables from the car's battery to avoid an electric shock.
  3. Use a hand pump to siphon the fuel from its tank into your container.
  4. Lift the car with a hoist so that you can work under the car.
  5. Place a carton under the car to avoid spilling oil on the asphalt.
  6. Detach the wires from the fuel tank while using a soft cloth to remove the tubes from the filler and the vent.
  7. Loosen the bolts, remove the tank's straps, then pull out the fuel tank.
  8. Place the tank near the drainage grills to start cleaning.

After you remove the fuel tank, you can now clean it. See these steps:

  1. Wear a mask and gloves.
  2. Pour lukewarm water into the tank to soften the fuel residue.
  3. Soak the tank with soap and scrub it with a brush.
  4. Apply a degreaser to eliminate the oil. Scrub again by frequently adding soap and water.
  5. Pour again with lukewarm water to finish the cleaning, then let it dry before putting it back in your car.

You may rub the fuel tank with a dry cloth or leave it in a dry place.

As mentioned earlier, a degreaser is a special solution meant to eliminate oily stains like fuel.

See this degreaser on Amazon.


Throughout this article, we have shown how to reset the DEF light and how significant the DEF is. We also provided details on what to do if you accidentally poured the DEF into the fuel tank.

We've discussed when to reset the DEF light and what to do if the lights on the dashboard don't glow.

Keep in mind that DEF is different from fuel. Refill the DEF so that you can continue utilizing your car.

Do you want to learn more from us? See these articles:

How To Replace Battery In Mercedes GLC Key Fob

How To Turn On Ambient Lighting Mercedes GLC

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