AdBlue is the essential additive for Euro 6 diesel engines with SCR (Selective Catalytic Reduction) technology: it reduces NOx by transforming them into nitrogen and water vapor , allowing the vehicle to comply with regulations and drive without restrictions. In this guide, I explain what it is , how it works , which warning lights and DTCs to monitor, how to perform a correct diagnosis , and which are the best brands to buy safely.
Useful Insight: AdBlue Problems on Peugeots: Here's What to Do on the 208, 308, 3008, and 5008
Last updated: September 11, 2025 · Edited by Gianni Tritella
🔧 What is AdBlue and how does SCR work?
By definition, AdBlue (also DEF – Diesel Exhaust Fluid ) is a solution of 32.5% high-purity synthetic urea and 67.5% demineralized water . It is injected upstream of the SCR catalyst where, thanks to the temperature of the exhaust gases, it decomposes into ammonia: this reacts with nitrogen oxides (NOx) to form harmless N₂ and H₂O .
Main advantages
- NOx reduction → lower emissions and compliance with Euro 6/6d regulations.
- Efficiency → the engine can be mapped for better performance/consumption, delegating NOx control to the SCRs.
- Access to low-emission areas (limited traffic zones, green areas) where applicable.
🧪 Why quality is crucial (ISO 22241)
Using AdBlue compliant with ISO 22241 is crucial: poor quality or contaminated products cause crystallization , injector clogging , pump failure and insufficient SCR efficiency .
- Impurities (salts, metals) → circuit obstruction and deposits.
- Out-of-specification urea → reduced reactivity, reducing quality DTC.
- Non-demineralized water → corrosion, false NOx sensors.
Golden rule: buy only sealed, ISO 22241-certified packages from trusted sources.
🚨 Warning lights and DTCs typical of the AdBlue/SCR system
When AdBlue or SCR are not working properly, you can find in diagnosis:
- P204F – Reductant System Performance (Generic AdBlue Malfunction).
- P20EE – SCR efficiency below threshold (downstream NOx too high).
- P207F – Reducing quality (AdBlue out of specification/contaminated).
- P20E8 – Low reducing pressure (pump/lines/filters).
- P2033/P2201 – NOx/Temperature Sensors Out of Range.
Warnings such as: “Refill AdBlue, failure to start in XXX km” or “Anti-pollution system fault” appear in the passenger compartment.
🔎 Step-by-step diagnosis (workshop method)
- Read DTC + freeze-frame → understand under which conditions the error is activated (remaining km, gas temp, load, speed).
- Check the AdBlue level and quality → verify the concentration and absence of contaminants (no tap water!).
- Actuator tests → pump priming , injector control, line leak check; pressure must fall within OEM values.
- NOx sensors → compare upstream/downstream readings; if the reduction is zero, suspect injection or catalytic converter.
- Visual inspection → glass around the injector, corrosion of connectors, cracked pipes.
- Exhaust thermals → if the temperature is too low, the SCR reaction is not effective (short urban use, DPF regenerations in progress, insufficient EGT).
❌ Common mistakes to avoid
- Using water or additives in AdBlue → you will damage the pump, injector and catalytic converter.
- Incorrect storage (direct heat or prolonged subzero temperatures without precautions) → quality deterioration.
- Pouring with dirty containers → instant contamination.
- Ignore the “failure to start in XXX km” warnings → risk of vehicle downtime.
🏷️ The best AdBlue brands (2025 selection)
Below are the reliable, ISO 22241-compliant brands mentioned in the article. You can find them in 10-liter containers with a convenient spout. Always check for seals , traceability , and the purchasing channel.
BASF — AdBlue 10 L
Purity and consistency reference: reduces SCR injector risks and crystallizations. Complies with ISO 22241 .
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YARA AIR1 — AdBlue 10 L
Premium brand with capillary mesh , also used in heavy transport. Canister with flexible spout. ISO 22241 .
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GREENCHEM — AdBlue 10 L (nozzle)
Focus on sustainability . Integrated spout for clean refills, reduced risk of contamination. ISO 22241 .
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TOTALenergies — AdBlue Clearnox 10 L
Consistent quality and excellent availability in the fuel network. Compatible with Euro 6 SCR systems. ISO 22241 .
🛒 Buy now on Amazon📦 Storage, expiration and safety
- Expiration : Typically 12–18 months if stored properly.
- Temperature : ideal -5°C → +25°C . AdBlue freezes at around -11°C (it recovers after thawing if not contaminated).
- Containers : only suitable plastic; avoid incompatible metal.
- No mixes : don't add water, additives or "improvements".
- Protect the paint : any drops should be rinsed off immediately with water.
📊 Quick table: AdBlue key data
| Parameter | Value/Note |
|---|---|
| Composition | Urea 32.5% + demineralized water 67.5% (ISO 22241) |
| Freezing point | About -11°C |
| Typical consumption | ~ 1–3% of diesel consumption (passenger use) |
| Duration | 12–18 months if stored at -5/+25°C, away from light/heat |
| Regulations | Euro 6/6d – NOx reduction requirements with SCR |
BEST ADBLUE 2025: BASF
Our editorial team has named BASF AdBlue the best AdBlue on the market for 2025 for its consistent quality, purity, and reliability in SCR systems for cars and commercial vehicles. It's the ideal choice for workshops and fleets looking to reduce the risk of crystallization, deposits, and injection problems.
Why he wins
- Controlled purity (32.5% automotive-grade urea): reduces the risk of impurities and SCR injector blockages.
- ISO 22241 compliance : chemical-physical specifications and packaging materials compliant.
- Batch-to-batch consistency : stable performance even in intensive use (city/highway, fleets).
- Careful packaging : sealed tanks, dedicated spout → less contamination when refilling.
- Wide distribution : availability and traceability useful for professionals and large users.
When to choose it
- Have you had AdBlue/SCR errors or deposits and want to minimize the risk of recurrence?
- Do you manage fleets or Euro 6 vehicles and are looking for consumable standardization?
- Choose sealed containers with a spout to reduce contamination from decanting.
Evaluation methodology
❓ Frequently Asked Questions
Can I drive without AdBlue?
Some vehicles allow low gear for a short time; however, a "failure to start" message will appear after XXX km . Refuel as soon as possible to avoid downtime.
Does expired AdBlue damage the system?
May cause reduced efficiency and quality DTCs (e.g., P207F). If you suspect expiration or contamination, drain and refill with new, certified product.
Why do I have P20EE even with a full tank?
The cause is not the level but the effectiveness of the reduction : check injection, pressure, crystallizations, NOx sensors and gas temperatures (too short cycles do not activate the reaction well).
Is it better to use a can or fill up at the pump?
Both solutions are suitable if certified to ISO 22241. The container with spout reduces the risk of contamination during decanting.
📌 Conclusions
AdBlue is the heart of the SCR system: quality and proper maintenance are crucial to avoiding warning lights, DTCs , and costly repairs. Choose ISO 22241 products, refuel cleanly, and don't ignore warnings: in most cases, methodical diagnosis restores efficiency without replacing the entire system.
1 comment
Sergio Ferrini
Uso AdBlue BASF da anni sia per la mia auto che per i mezzi della mia azienda e posso dire che non mi ha mai dato problemi. La qualità si vede: niente cristalli, niente odori strani e soprattutto il sistema SCR funziona sempre al meglio, anche nei mesi più freddi. Ho provato in passato altri marchi, ma con BASF ho trovato una costanza che mi ha convinto a non cambiare più. Per me rimane la scelta più affidabile, soprattutto se si vuole stare tranquilli nel lungo periodo.