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A typical dishwasher normally has a motor that runs either in a single direction or is capable of running both forward and backward. Units with reversing motors use the motors to drain water from the system. Those with motors running only in a single direction typically use a drain valve connected to a dishwasher solenoid to empty the water.
A dishwasher solenoid stores electricity. When it receives the appropriate signal from the machine’s control cycle, the solenoid uses the stored power to move a lever. The lever is attached to the gate portion of the valve, which opens to let water pass or closes to keep water in.
One of the easiest ways to determine if a machine's motor operates in a single direction or is capable of reversing is by counting the wires attached to the motor. If there are two or three wires, it runs only in a single direction and the unit will have a dishwasher solenoid. Systems with four wires have motors that can run in reverse, allowing the unit to drain water with the motor, and it will not have a dishwasher solenoid.
When a dishwasher solenoid is working properly, the machine fills and drains as it proceeds through the various cycles. If there is a problem with the solenoid, some or all of the water will remain inside when it is finished running. This may be caused by failure of the dishwasher solenoid, the timer or the electrical connections to the solenoid.
Since the solenoid is an electrically-operated part, a broken or corroded wire can cause it to fail. A visual inspection prior to removing the part can help to identify obvious wire problems. Loose or discolored wires, damaged insulation or corroded connectors can all be responsible for electrical failure. It can be helpful to check for other obvious problems at the same time, such something blocking the drain.
If nothing turns up in a visual inspection, the dishwasher solenoid should be removed from the machine for further inspection. An ohmmeter can be used to check for electrical continuity. If the part has continuity, it should be checked to make sure the lever on the solenoid that opens and closes the gate is able move freely. Should everything seem to be in working order, the draining problem may be caused by something else, such as a clog down in the drain pipe. If the solenoid fails any part of continuity testing or visual examination, it should be replaced.