Diagnosis
'SUD' is a suds lock error. You used too much high-efficiency detergent or the wrong type, creating excessive suds the washer can't rinse out.
How to Fix It
Press Pause/Cancel twice to clear the cycle. Open the door. Add 1/2 cup of white vinegar directly into the drum. Close the door. Run a rinse and spin cycle. The vinegar will break down the excess suds. Use only 1-2 tablespoons of HE detergent per load.
If That Didn't Work
The pressure switch (water level sensor) or its tube might be clogged with detergent residue, giving a false suds reading. A technician would need to check the tube for blockage and clean it.
Heads Up
Never use regular (non-HE) detergent in a front loader. It creates massive suds. Using more detergent than recommended does not clean better; it causes this error and leaves residue on clothes.