There are two main methods: objective fault diagnosis and subjective fault diagnosis. The objective fault diagnosis method is a method of diagnosing faults through special measuring tools, instruments, equipment, etc. It is relatively complicated to use, and is mainly used for fault diagnosis at professional repair shops with a certain scale. The subjective fault diagnosis method is to diagnose faults by seeing, hearing, sniffing, and touching by hand. It is simple and easy to use, and is more suitable for use by the robot. Therefore, this article focuses on the subjective fault diagnosis method:

　　(1) Use the "eye to see" visual inspection. Directly observe the abnormal phenomena of agricultural machinery with eyes, such as oil leakage, water leakage, smoke from the engine, loose parts, obvious fractures, and distortions.

　　(2) Use "ear hearing" sound test. Judge the fault location according to the characteristics of the sound, distinguish the abnormal sound and accompanying sound that should be noticed when the fault occurs, pay attention to the relationship between the sound and the speed, temperature, load and the position of the sound, and improve the accuracy of judging the fault. For example, engine piston knocking is related to speed, load and temperature. When the speed and temperature are low, the sound is clear; when the load is heavy, the sound is obvious.

　　(3) Adopting “nose smell” odor inspection: according to the characteristics of odor to determine the location where the fault may occur, and distinguish the abnormal odor and accompanying smoke that should be noticed when the fault occurs. Such as the rubber smell of the belt, the burning smell of the friction plate, etc., there will be obvious abnormal smells.

　　(4) Use "hand touch" tactile test: touch the suspected fault or the part related to the fault with your hand to find the fault. If the brake drum is hot when touching the brake drum with your hand, it indicates that the wheel brake has a brake blocking failure.