Transmission diagnostic tools are mechanical and computerized devices that allow an individual to communicate with a vehicle's on-board diagnostic system and gather information about potential issues. The term can be applied to a variety of devices, ranging from manual pressure gages to digital readout displays.
Before using a transmission diagnostic tool on a vehicle, it is best to perform a manual test to see if the issue is with the transmission or the engine. One common test involves placing the vehicle in either reverse or drive, then putting the parking break in place to prevent any vehicle movement. Once the brake is set, the individual places her foot on the gas for a few seconds to see the engine's RPM readout. If the RPMs hold steadily between 1,500 and 3,500, the issue is likely with the transmission, as a malfunctioning engine typically cannot maintain that performance level.
Certain types of digital transmission diagnostic tools come in both general and manufacturer-specific varieties. A general diagnostic tool is capable of understanding a limited amount of information from a broad range of vehicles, while manufacturer-specific tools can only be used on certain vehicles, but these tools can understand a greater breadth of information.