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OBD systems are provided for the use of the owner of the vehicle as well as repair technicians.

OBD system is merely reporting to the user what the various sub systems are saying. The user is completely isolated and not privy to the conversation. Such is the case when reading DTCs and PIDs.

In reporting mode OBD cannot alter anything in the vehicle being monitored, let alone stuff up a speed sensing system. OBD is in widespread use by many many vehicle owners users worldwide.