The ‘AdBlue Level Low’ warning in Mercedes-Benz vehicles is related to the Selective Catalytic Reduction (SCR) system, which reduces nitrogen oxide (NOx) emissions in diesel engines. AdBlue is a urea-based solution that is injected into the exhaust to convert harmful gases into nitrogen and water vapor. When the AdBlue level is low, the vehicle may display warnings such as ‘AdBlue Level Low’ or ‘Refill AdBlue – No Start in XXX km.’ This article explains what the warning means, common causes, how to refill AdBlue, and when to seek professional service.
What is AdBlue?
AdBlue is a high-purity urea solution (32.5%) used in the SCR system of diesel Mercedes-Benz vehicles. It is stored in a separate tank and injected into the exhaust gases before they reach the catalytic converter. This reduces NOx emissions and ensures compliance with Euro 6 and other environmental standards.
Common AdBlue-Related Messages
When the AdBlue level drops, you may see messages such as:
• AdBlue Level Low – Refill Required
• Refill AdBlue – No Start Possible in XXX km
• AdBlue System Fault (if there are sensor or pump issues)
Causes of AdBlue Level Low Warning
The most common causes include:
1. Naturally low AdBlue level due to consumption over time.
2. Failure to refill AdBlue during routine maintenance.
3. AdBlue leaks from the tank, lines, or injector.
4. Faulty AdBlue level sensor inside the tank.
5. Crystallization of AdBlue in cold temperatures causing blockages.
6. Software or SCR ECU errors.
How to Diagnose AdBlue Warnings
Start by checking the AdBlue level in the dedicated tank. If it is low, refill with certified AdBlue fluid (ISO 22241 standard). If the warning persists after refilling, a diagnostic scan using Mercedes-Benz tools such as Xentry, Vediamo, DTS Monaco, or the MBCOD Box with ELM327 should be performed to check for SCR system fault codes. Common codes include P20xx (AdBlue injector issues) or P207F (low AdBlue quality).
How to Fix AdBlue Level Low Issues
Steps to resolve AdBlue warnings include:
1. Refill the AdBlue tank with fresh, Mercedes-approved AdBlue fluid.
2. Ensure the filler cap is properly closed to prevent contamination.
3. Repair leaks in the AdBlue tank, injector, or lines if present.
4. Replace faulty AdBlue level sensor if it gives false readings.
5. Clean crystallized deposits around the injector or filler neck.
6. Update or reprogram the SCR ECU if necessary.
7. Clear any stored fault codes and verify the warning disappears.
Preventive Maintenance for AdBlue System
To prevent AdBlue warnings, regularly check and refill AdBlue before long trips, use only certified AdBlue fluid, and avoid storing AdBlue for extended periods as it can degrade over time. During winter, ensure the AdBlue heating system is functional to prevent crystallization.
When to Contact a Specialist
If the ‘AdBlue Level Low’ warning persists after refilling, it may indicate a sensor or SCR system fault. At MBCOD in Dubai, we provide expert diagnostics, AdBlue tank and injector repairs, SCR ECU programming, and complete emission system servicing. We also offer mobile support across Dubai, Abu Dhabi, Sharjah, and Ajman.
Conclusion
The ‘AdBlue Level Low’ warning is a reminder to maintain the emission-reduction system in Mercedes-Benz diesel vehicles. Ignoring it may eventually prevent the vehicle from starting. By refilling AdBlue on time and servicing the SCR system when necessary, you can ensure compliance, performance, and reliability. Trust MBCOD in Dubai and across the UAE for expert AdBlue system diagnostics and repairs.