Which terminal serves as the signal ground for all vehicles in the OBD-II data link connector?

The correct choice is based on the function and designation of the terminals in the OBD-II data link connector. Terminal 5 is specifically designated as the signal ground, which serves as a common reference point for all signals in the diagnostic communication framework of OBD-II systems. This terminal is crucial for grounding and ensuring consistent voltage levels for the Electronic Control Units (ECUs) when they communicate with diagnostic tools.

Having a dedicated signal ground helps minimize noise and signal interference, which is particularly important in the automotive environment where multiple electronic components operate simultaneously. This allows for more reliable data communication during diagnostics and troubleshooting.

Understanding the role of terminal 5 as the signal ground is fundamental for technicians and students studying automotive electrical systems, particularly when working with diagnostic tools to interface with OBD-II systems.