If the problem is poor cleaning, monitor the water fill period, should be more than 40 seconds to fill up near the heater. If not over 40 seconds you may have a bad timer. If ok, check the water solenoid screen for partial clog, if ok replace it.
To confirm water level problem, you can add a few gallons of water to the tub and check for "normal " operation. Confirm you have clean holes in all spray arms and that they turn during wash
You can confirm this by opening the door while it's washing and check the spray arms for motion.
Next, turn water supply off, remove torq screws holding the upper filter housing and remove the half round pump cover and sponge out all the water.Clean the cover. If it has a chopper and screen, check for a clogged screen. If clogged install a new chopper and check valve on the bottom of housing.
Turn the chopper in front of the screen, if free to turn, you either have a bad chopper or busted motor impeller. Pull out chopper assembly to check.
If ok, add a little water, and verify pump is pumping. If a Frigidaire, you can see if the pump is turning the impeller the right way, if not, your pump motor is polled and must be replaced.
If turning the right way, you might have a broken impeller. Pull the dishwasher and pump to check.