My Land Rover/Range Rover is Telling Me to Top Up the DEF – What is It and How Do I Refill It?
13/11/24
If you own a Land Rover or Range Rover, you may have seen a message on your dashboard instructing you to "Top Up DEF" or something similar. If you’re unfamiliar with DEF (Diesel Exhaust Fluid), you might be wondering what it is, why your vehicle needs it, and how to go about refilling it properly. In this guide, we'll cover everything you need to know about DEF and why it's important not to overfill it.
What is DEF?
Diesel Exhaust Fluid, also known as ADBLUE, is a non-toxic, colourless liquid made up of 32.5% urea and 67.5% deionized water. DEF is used in vehicles equipped with Selective Catalytic Reduction (SCR) systems to reduce harmful nitrogen oxide (NOx) emissions from diesel engines. When injected into the exhaust stream, DEF helps break down NOx gases into harmless nitrogen and water vapor, making your vehicle more environmentally friendly and compliant with emissions regulations.
Why is My Range Rover Asking Me to Top Up DEF?
Your Land Rover or Range Rover has a dedicated DEF tank, and when the fluid level gets low, your vehicle will alert you to top it up. If you ignore the warning and let the DEF level drop too low, your vehicle may enter a restricted performance mode or even refuse to start until the DEF has been replenished.
Important: Confirm the Message Before Topping Up
Before adding DEF, ensure that the message on your dashboard is asking you to "Top Up DEF." Sometimes, owners confuse this with a different message stating, "DEF Quality is Poor." If you see this message, it means the fluid is either contaminated or of very poor quality and simply topping it up will not resolve the issue. In such cases, you may need to drain the DEF tank and refill it with high-quality DEF that meets ISO 22241 standards. (This work would have to be carried out by professionals, and the system would need to be reset.)
How to Top Up DEF in a Land Rover/Range Rover
Topping up DEF is a straightforward process. Here’s how to do it:
- Locate the DEF filler cap – The DEF filler cap is typically located next to the diesel fuel cap or under the bonnet, depending on your vehicle model.
- Purchase the right DEF – Always use high-quality DEF that meets ISO 22241 standards. You can find DEF at fuel stations, auto parts stores, or Land Rover dealerships.
- Use a proper filling method – DEF is sold in bottles with special nozzles to prevent spills. Avoid using open containers to prevent contamination.
- Slowly pour the DEF into the tank – Follow the manufacturer’s recommendations for the correct amount to add.
- Do not overfill! – Your vehicle may not accurately read the fluid level if the tank is overfilled, potentially causing system errors or overflow. So always fill a little under the recommendation to be on the safe side.
- Replace the cap securely – Once you have finished topping up, make sure the DEF cap is tightly closed to prevent contamination.
Why You Shouldn't Overfill the DEF Tank
Many Land Rover and Range Rover owners have heard that they shouldn't completely fill the DEF tank, but why is this the case?
- System Calibration Issues – The DEF system relies on sensors to measure the fluid level. If the tank is overfilled, the sensors may not register the correct level, leading to inaccurate warnings or error messages. (Our advice would be to never put more than 10 litres in) drive the vehicle for 3 drive cycles to confirm the system has reset.
- Overflow and Spillage – DEF expands slightly in temperature fluctuations. Overfilling can cause the fluid to spill out, leading to potential damage or crystallization around the filler area.
- Manufacturer's Guidance – Land Rover specifically recommends against overfilling the DEF tank to ensure optimal system performance.
Conclusion
Keeping an eye on your DEF levels is essential to maintaining your Land Rover or Range Rover’s performance and emissions compliance. When you see the "Top Up DEF" warning, make sure to refill with high-quality DEF, follow the correct procedures, and avoid overfilling the tank. Also, double-check that the message is actually a "Top Up DEF" warning and not a "DEF Quality is Poor" alert, which indicates a different issue requiring a workshop visit to investigate the issue. By doing so, you’ll ensure your vehicle runs smoothly and efficiently while helping to protect the environment.
If you’re not sure about any of this and would rather it was checked for you, please call Newbury 4x4 Centre on 01635 32028