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.

When opening the filler cap of the DEF tank 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.

    See also:

    Purity
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    Cleaning the wiper blades
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    Hazard warning lamps
    Hazard warning lamps The hazard warning lamps automatically switch on if: • an air bag is deployed. • the vehicle is slowed down severely from a speed of over 45 mph (70 km/h) and comes to a ha ...