Its likely to be one of the following
a) a partially blocked drainhose
b/ the solenoid on the drain valve not opening closing probably
c) a blocked drain valve with a piece of bone or debris
This article should help you:
The main parts of a dishwasher are:
The control mechanism is located inside the door behind the control panel. Many units use a simple electro-mechanical system: a timer determines how long each part of the cycle lasts and activates the proper function at the proper time (such as the detergent dispenser, wash spray and draining functions). Units that are more expensive might have a computerized control system. Modern units also have a door latch that must be closed for the unit to run. Some also have child safety locks.
This is where water from the home's water supply enters the dishwasher. The unit's pump doesn't pump the water into the basin – when the intake valve opens, water pressure drives the water into the unit.
An electric motor powers the pump. During the pump cycle, the pump forces water up into the spray arms. During the drain cycle, the pump directs the water into the drain hose. The motor-pump assembly is mounted beneath the basin, in the center of the dishwasher. There are two main types of pump:
These pumps switch between pumping water to the spray arms and pumping water to the drain by reversing the direction of the motor. Reversible pumps are usually vertically mounted.
The motor runs in one direction, so the direction of flow is switched from spray arms to drain by a solenoid that opens and closes the appropriate valves or switches one hose connection to another. Non-reversible pumps are usually horizontally mounted.
Dishwashers can be installed in either a portable or a permanent configuration. Portable units have finished sides and top that can be used as a countertop. When not in use, the machine sits in place next to the wall. When it's time to run a cycle, the unit can be rolled on casters over to the sink, where it connects to the faucet and plugs into a nearby outlet. In a permanent installation, the dishwasher goes underneath the existing countertop and bolts into place. Hoses underneath the kitchen sink connect directly to the hot water line and the drain line, and the unit usually plugs in under the sink as well. Both types of installation require a 120-volt grounded line.