Remove the front panel....disconnect wires leading to soap dispenser ohm test the dispenser with wires disconnected it should read infinity for a complete circuit meaning the dispensor is good in most cases. Alot of manufactures make those with wax motors that are really cheap and break easily. If it reads 0 on your ohm check close the dishwasher door take the disconnected wires and run them to your voltmeter and start the dishwasher up and if you get 120v on those wires (typically within 3-10 minutes of starting then your main board should be ok and replace the dispenser itself. If you do not have 120 going to the soap dispenser usually within 10 minutes it's a bad main board most likely or a loose connection or bad wire leading to dispenser. Models do vary on what time the soap dispenser opens so check your tech sheet which is usually behind the very bottom panel under the unit. Good luck

They usually sell the dispenser and gasket as one solid piece and they typically won't sell the motors in them alone. Plus also it's just wiser to replace the whole thing because the release mechanism gets damaged over time being plastic with heat and water present all the time.