What does the 'SUD' code mean and what should I do when it appears?

The 'SUD' code means excessive suds have been detected and a suds routine has automatically started to remove extra suds and ensure proper rinsing. The code is displayed during rinsing and at the end of the cycle to inform you the routine was activated. To prevent this, use only HE (High Efficiency) detergents. (Page 20)