The breaker keeps popping. Replaced breaker and new breaker does the same. Dishwasher only appliance on this circuit. Has worked fine for 3 years. Where should I start to look for a solution.

Grounded hot or neutral wire or jammed motor. Look for worn or abraded insulation. Check the connection box under the DW. Make sure the motor is free.

Get a meter and learn to use it, then turn off power and disconnect it. Start from hot wire and trace circuit until you find short.