The dishwasher needs basic maintenance a few times a year. Most people find this out after finding specks stuck to plates or residue in mugs. Like any appliance, gunk builds up over time, requiring dismantling of parts to get a deep clean.
You will need a headlamp, vinegar, dish soap, a tough sponge, a screwdriver and kabob sticks. First, remove everything from inside the dishwasher, including:
The drain is bolted down, so you may need to hunt down the correct tool to undo it from the bottom. This is when you will find what is causing problems. Take the kabob and begin chipping away at the big stuff; food scraps, silverware and soap scum may be hiding. Get in there with your headlamp! Next, scrub with the sponge and hot soapy water, getting all the cracks that still have residue around them.
Last, run the dishwasher on hot with one cup of vinegar instead of dishwasher soap. You also might want to check the racks and spinner to ensure they are working properly and wiped down if needed.