Transmission oil is an oil-based product that keeps the gear shifting system clean. It can lubricate and extend the life of the transmission. It can also perform extremely effective lubrication under low temperature and low temperature, and reduce oil loss under severe operating conditions. The  automatic transmission is an important part of the automotive transmission system and the most sophisticated component. In case of problems, the repair cost is expensive.

The viscosity of the transmission oil will become thinner, resulting in decreased lubrication performance, decreased sealing performance, increased resistance and increased wear, resulting in unstable pressure, affecting hydraulic system operation accuracy, reduced gearbox control accuracy, reduced shift accuracy, and smoothness. Sex and response speed will be affected. After the deterioration, the oil cooling performance and anti-oxidation performance will be degraded, and problems such as excessive oil temperature will occur, and the vicious cycle will further shorten the life of oil and transmission parts. In general, the manufacturer's time limit for replacing the automatic transmission oil is recommended at 60,000 km or 4 years.