Water pooling in the bottom of your dishwasher is a sign that the drain pump might not be working. But the only true way to know is to use a multimeter to measure the drain pump's voltage, current, and resistance. First, remove the drain pump. Then, connect the multimeter to the terminals on the drain pump. The meter should show 15 to 40 volts of resistance if the pump is operating correctly. If the meter shows minimal change (or no change), the pump doesn't have electrical continuity. In that case, you'll need to replace the drain pump. This video provides a helpful tutorial on how to check if your dishwasher drain pump is not working.