Dishwasher Drain Pump: How to Test?

I have the same problem you had. I am not sure of the proper impedance you should have. One internet repair place says 200 ohms for a good motor. I did the same thing you did (same problem - dishwasher not draining) lines were clear to disposal - I also exercised the check valve which is in the 90 degree black elbow right off the drain pump on my machine (Whirlpool model WDF760SADM) forward and backward to ensure it flowed and would stop flow in the reverse direction, which it did. I do not have leads that are compatible with the motor to check that it runs. I am going to replace the drain pump to see if that is the problem. Also, the jerky motion on the impeller is due to the magnetism on the motor.

For future reference, before you take the thing out:

Unplug and replug the power and switch it on. Three things should happen in a reasonably modern dishwasher.

1. Power light will become bright

2. The water inlet sensor will either open or fail-close on pressure of inlet water. Closed switch means no power to dishwasher.

3. The drain pump will do one or two revolutions at minimum

It can be the water inlet sensor or the water inlet pressure that is fouling up. Since the sensor is fail close it should get hot to the touch (by just a few degrees, don't worry) over time if it is working. So check that it gets warm. Some models also have lights to indicate SENSOR OK, that saves a bit of waiting. If that isn't working, check the water on the inlet side. Remember you have to power down the machine with the plug to reset the switch, if you find you have a valve closed. If the water is fine, the sensor is fine, the drain swamp is reasonably clean, and still no "chugs" from the pump - take it out for manual testing.

Any leakage or failure to run should be considered graveyardable offenses. It just isn't economically reasonable to do anything else than getting a working one - scrap dealers usually have tonnes of them.

With the pump still on the machine:

1. Use a multimeter on the continuity setting check each lead to see if either one has continuity to the frame of the machine. If it does, that is bad. This is an unlikely culprit.

2. Put the multimeter on the ohms setting. Put the probes on the two motor contacts. Anything in the 10s to 100s of ohms should be considered good. If it is higher than hundreds, it is possibly bad.

If it passes those tests, remove the pump and attach 120v AC (or whatever the specs say on the label on the pump depending on the country you live in). You can do this by taking an old power cord from a junk appliance, tool, or light and stripping the ends of power and common. Attach them to the motor leads and plug it in keeping hands away from those wires. If the impeller spins it is good. If it doesnt spin it is bad.

If it spins, Id suggest looking into the impeller housing- there may be a small chip of glass or ceramic in there that could be jamming the impeller.

Dishwasher was not draining completely. Checked hoses and found them to be clear. Could not hear pump running as was usual when starting a cycle. I was about to order a new pump when I decided to see if the check valve was operating properly. The valve was fine but I did notice that the impeller was difficult to turn. Further investigation revealed a chunk of ceramic pottery that had become wedged between the impeller housing and the impeller. Removal of the piece of pottery restored the dishwasher to normal operating condition.

Not taking the dishwasher out, able to reach the pump, diconnecting and removing it, I then took my wet vac and connected it to the end of the discharge hose. Then using the blow side of the wet vac tried to blow forward breaking up the blockage. This not working using the vac side broke the blockage and about a gallon of water that was traapped. Put everything together disshwasher worked fine.

For future reference. You can try removing the hose casing from the pump motor and clean the motor around the propeller throughly and Lubricate then turn the propeller manually a few turns to get anything that may be jamming it out then reconnect. If it’s receiving electricity (making a humming noise) but not turning, chances are that something is stopping it from rotating.

Make sure you check the pipes connected to the drain hose going to your sink. We FINALLY found that the connection from the drain hose to the PVC pipe was corroded and completely blocked. Dishwasher is running fine now...3 weeks later.