A system and method for diagnosing a home appliance are disclosed. The home appliance outputs product information as a predetermined sound signal, and transmits the sound signal to a service center of a remote site over a communication network, such that a service technician of the service center can easily check a current status of the home appliance. When a diagnostic server of the service center analyzes the sound signal of the home appliance, it selects a plurality of preamble candidates and can effectively and correctly detect data using weights, so that it can quickly diagnose a faulty operation of the home appliance. An erroneous data analysis and its associated erroneous diagnosis are prevented, so that the diagnostic system provides a service for more correctly diagnosing a faulty operation of the home appliance and also increases user satisfaction and reliability of the home appliance.