To test the dishwasher check valve, also called a drain check valve, the machine must be unplugged from the power supply, the access panel needs removed and the valve located for testing of the solenoid. Items needed include a screwdriver, needle-nose pliers and a multi-tester.
The check valve is usually found where the pump and/or the motor attaches to the drain hose. The easiest way to find the valve is to look for the water hose that is attached to the motor or runs under the tub. The valve's main function is to prevent used water from going back into the dishwasher after it's been drained. A stuck valve prevents the dishwasher from draining properly.
The valve has a gate arm mechanism, which should move back and forth easily. The gate arm has two springs that sometimes need replacement. The drain line solenoid controls the gate via two wires that deliver an electrical charge. To check the solenoid, pull the wire connectors off and test with a multi-tester.
This device has two probes and a read-out screen that check for electrical resistance, or the rate at which electricity flows through the solenoid. When both probes touch the terminals at the same time, a working solenoid should read roughly 40 ohms. Otherwise, it needs replacement.