Dave, according to the service manual there are a few possibilities

Sud - SUDS LOCK (Overdose of Detergent detected during the Wash Cycle)

The motor control unit senses a suds lock condition by analyzing the current draw on the drive motor. If “Sud” is displayed a potential suds lock is detected. This may signify a bad pump, an extra heavy load, excessive detergent, or excessive suds.

• If too much detergent was used, run the unit through a Rinse/ Spin cycle then a Normal cycle without adding any detergent. This should clear the unit of the excess detergent.

• Check the drain hose and make sure it is not plugged or kinked

• Check Wire Harness connections to the Drain Pump, Pressure Switch, and Central Control Unit (CCU)

• Check/ Clean Drain Pump Filter of foreign objects

• Check Drain Pump

• Check the Pressure Switch

• Check CCU

To make your job easier, try to download the manual from the bottom of this page Good luck and I hope it helps.

Here is an image showing the location of the pressure switch