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The vehicle parameters (PIDs) that are available on the OBD2 port of a vehicle are quite limited. And also they vary from vehicle to vehicle - both the count and parameter set itself. Have two questions in this regard:

  1. On what basis the car maker (OEM) determines, what and how many PIDs they are exposing on the OBD2 port?
  2. Is there another way out to read/access larger set of vehicle parameters from a vehicle?
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The data available on the ODB port is a combination of the data required by the law in the country where the car is sold and the data that the vehicle maker wants to expose for diagnostics and tuning.

It's worth pointing out, I think, that the PIDs aren't necessarily there and not exposed in all cars. Vendors choose what data to expose and in many cases the data simply isn't there or doesn't make sense in the context of the particular vehicle (e.g., automatic transmission related data on a car with a manual) or steering angle on a car without a steering angle sensor. The list of standard PID values exists to help bring order to the industry and assist regulators and repair shops – it's not a list of what can or should be implemented (except in the case of the data that is legally mandated).

Beyond the data that is mandated by the local authorities, the data and the tools to read the data are often proprietary – or maybe it would be better to describe them as "not publicly documented," since in this day and age any vendor who wanted to truly protect their data and interfaces would probably use encryption. Arguably they should be using encryption to help guard against attack.

  • Thanks much! here is some further point, I want to clarify - when using generic OBD2 reader dongle (say from Scantool, or Ford OpenXC, ...), it providers the generic standard PID parameters (in certain no as exposed by car maker); If we want to read/access the proprietary parameters of the specific car, how can we do that? are there such tools / software available OR that could be done in consultation with the car maker itself? – Akhilesh Gupta Nov 20 '16 at 8:20
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There are usually some basic ones to match smog law requirements for different countries but really any car manufacturer can put whatever sensors they want on their computers. So there really isn't a standard per se. The standard is in regard to what code gets thrown for which sensor.

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Yes, there is a larger set available on newer vehicles, but usually you need special software to read these values. They are hidden in the proprietary layers of the protocol or in the CAN bus. Ford/Mazda have their own system called WDS. GM has another. BMW/Mini use yet another. Some phones now can access these parameters via an OBDII reader if the reader supports extended parameters.

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