Anti-Crystallisation Additives: What They Change for Your Legal Guarantees

For every diesel vehicle equipped with SCR, a recurring question is whether an anti-crystallisation additive invalidates the warranty. The answer is not a blanket yes. AdBlue is defined by ISO 22241 as 32.5% urea and 67.5% demineralised water. Anti-crystallisation additives are freely sold. At the recommended dose, around 10 ml per 10 litres, or 0.1%, the fluid remains within ISO 22241. Pre-additised AdBlue is even sold in 210-litre drums and 1,000-litre IBC containers. What takes the fluid out of specification is overdosing: two to three times the recommended dose changes its composition and can clog the SCR system with deposits.

Three warranties that are not the same

Under French law, three warranties must be distinguished.

• Legal conformity warranty (Consumer Code, art. L217-1 and following). It is owed by the seller, and it is a matter of public policy. Any clause that excludes, shortens or limits it is deemed unwritten. No additive can cancel it.
• Latent defect warranty (Civil Code, art. 1641). It covers a defect that existed before the sale. A product poured into the tank after the purchase does not remove that warranty.
• Commercial warranty from the manufacturer. It is a voluntary contract, so it may exclude non-approved products. It can never reduce the legal warranties.

What an additive actually changes

An additive does not void legal rights. What it can do is give the manufacturer a causality argument: detect an additive and claim the failure came from the fluid rather than from the design. That argument is contestable; it does not close the discussion. This is why, during an ongoing claim or legal procedure, the cautious choice is to abstain: not because the product is illegal, but because it offers an unnecessary technical argument to the other side.

The practical rule

• If a claim or proceeding against the manufacturer is under way, do not use the additive for the time being.
• If the vehicle is outside commercial warranty and no claim is being made, there is no legal risk in using the product at the prescribed dose.
• Always respect the dosage. Overdosing is what can damage the system, not the additive.

Consumer protection law and latent defect law remain the relevant legal basis. If you have experienced an AdBlue or SCR failure, please add your case to our registry. The more documented cases, the stronger the file.