1. Subjective diagnostic technology: it refers to the maintenance personnel using simple diagnostic instruments to analyze and judge the causes and locations of four-column hydraulic press failures based on their personal practical experience. It is convenient and fast and has low reliability. It belongs to simple qualitative analysis, including the intuitionistic empirical method, logical analysis method, parameter measurement method, cut-off method, and so on.

1) Intuitive experience method refers to the maintenance personnel with their senses and experience, through seeing, listening, touching, smelling, asking, and other methods to determine the cause of failure.

2) Logic analysis method refers to the logical relationship and fault phenomenon of four-column hydraulic press components, systems, and equipment, through the study of hydraulic schematic diagram and component structure, logic analysis, to find out the fault location.

3) Parameter measurement method means to determine whether the parameters are normal or faulty by measuring the working parameters at the required points in the system loop and comparing them with the normal working value of the system.

4) Cut-off method refers to the composition of the hydraulic press system and fault phenomenon selection cut-off point, cut-off method is to observe the change of pressure and flow, so as to find out the fault method.

2. instrument diagnosis technology: according to the pressure, flow, temperature, noise, vibration, oil pollution, the speed of the execution parts of the hydraulic press system, through the instrument display or computer calculation to judge the results.

3. Intelligent diagnosis technology: it refers to the simulation of human brain function, the effective acquisition, transmission, processing, regeneration, and utilization of fault information, and the use of a large number of unique expert experiences and diagnosis strategies.