DEF

Important safety notes

For BlueTEC vehicles only.

DEF is a non-flammable, non-toxic, colorless, odorless and water-soluble fluid.

Rinse surfaces that have come into contact with DEF immediately with water or remove DEF using a damp cloth and cold water. If the DEF has already crystallized, use a sponge and cold water to clean it. DEF residues crystallize after time and contaminate the affected surfaces.

High outside temperatures

If DEF heats up to over 122 °F (50 °C) for extended periods, e.g. as a result of direct sunlight on the DEF reservoir, DEF can decompose. Ammonia vapors develop as a result.

WARNING
When opening the filler cap of the DEF tank ammonia gas vapors may escape. Refill DEF in a well ventilated area only. Ammonia gas vapors have a pungent odor and are particularly irritating for your skin, mucous membranes, and eyes. Inhaling ammonia gas vapors will cause burning eyes, nose, and throat, as well as coughing and watering eyes.

Low outside temperatures

DEF freezes at a temperature of approximately 12 °F (–11 °C). The vehicle is equipped with a DEF preheating system when it leaves the factory. Winter operation is therefore also guaranteed at temperatures below 12 °F (–11 °C).

Additives

Only use DEF in accordance with ISO 22241. Do not use additives with DEF and do not dilute DEF with water. This may destroy the BlueTEC exhaust gas aftertreatment system.

Purity

Assuring the purity of DEF is particularly important with respect to avoiding malfunctions in the exhaust gas aftertreatment system.

If DEF is pumped out of the DEF tank, e.g.

during repair work, it must not be returned to the tank. The purity of the fluid can no longer be guaranteed.

Impurities in DEF (e.g. due to other service products, cleaning agents or dust) lead to:

 - increased emission values
 - damage to the catalytic converter
 - engine damage
 - malfunctions in the BlueTEC exhaust gas aftertreatment system

    See also:

    Problems with the SmartKey
    Problem Possible causes/consequences and Solutions You cannot lock or unlock the vehicle using the SmartKey. The SmartKey battery is discharged or nearly discharged. ...

    Top Tether
    WARNING Always lock the rear seat backrests in their upright position when the rear seats are occupied by passengers. Lock the rear seat backrests in their upright position before installing ...

    M+S tires
    At temperatures below 45 °F (+7 °C), use winter tires or all-season tires. Both types of tire are identified by the M+S marking. Only winter tires bearing the snowflake symbol in addition t ...