Originally Posted by wstar

Well, to be more precise, aftermarket OBD-II tools read live data via the standard semi-open protocols. They also read a few other things, like freeze frame data from logged faults (e.g. if you had a cylinder misfire, you could pull up a snapshot of all sorts of info, including vehicle speed, from the moment of the misfire). They're not actually "ECU readers". Those tools know virtually nothing about the car's ECU or what's stored inside of it. They just get to talk to it and hear what it wants to say to them.

Nobody but Nissan really knows every little detail of what else our ECU does that isn't available over the standard mechanisms. There might even be things tucked away in there that normal dealership Consult tools can't access, but certain authorized people (factory representatives? acting on behalf of law enforcement in a major case?) can access with special Nissan software.

But none of that is going to help you with a speeding ticket, sorry.