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ATP: How OBD2 Works

Want to get started with car hacking? This video is for you!

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Greetings and welcome to June! In this episode of ATP, I’m going to cover everything I consider required information about OBD2 to enable you to start poking around at the innards of your car’s data bus. We’ll do a brief history about why it exists at all, talk about the assorted buses and pinout of that oh-so-famous connector, cover the command structure, present examples and wrap up with an evaluation of how you might want to proceed (including some gear choices). I'll also point you toward more info to take you further.

Stuff you should read:

Gear that I talk about:

Comments 8 comments

  • Big pat on the back for this one Pete. Well done and thank you!

  • Is there somewhere we could see this in text form, say a transcript file?

    • All I have are my notes, and that wouldn't be pretty. They're really chaotic and spread amongst various media...

  • Very nice

  • FWIW, I just got back from having my car (a 2013 Dodge Dart) emissions tested (in the Phoenix area). All they did was to plug into the OBD2 connector, observe that when they switched from "START" to "Run" on the key that the "check engine" light came on briefly (to indicate that it was working) and then went off, and their computer "interrogated" the OBD2 stuff on the car. Oh, and they checked the gas cap for leaks. (And charged me $17.). It passed the test, so it's good to go for another two years.

  • Another interesting ATP!

    Looking through the PIDs again, I still don't see anything that's the "true" odometer reading -- disappointing for my needs. I suppose I could use 0x31, distance (in km) since codes cleared, but that only goes to 65,535 (roughly 39,000 miles). It seems to me that rather than "rolling over", the way it should behave is to "stop counting" when it gets to max. I suppose that one way to deal with this would be to (intentionally) leave the gas cap off for a couple of km (that brings on the "check engine" light). I think that one will self-clear when you put the gas cap back on...

    Oh, yes, one minor argument: it seems to me that the CARB (California Air Resources Board) can only (directly) control vehicles sold in California. However, since CA represents a significant chunk of all cars sold in the US, it's often easiest for the manufacturers to make all cars comply rather than just those destined to CA (and then having to make sure that non-CA cars don't get shipped to CA). (Yeah, I know that several of CARB's standards have been adopted into national standards, but they started out as "required in California only".)

    • Regarding the gas cap, my car will shut off the engine light after 3 consecutive times not having the fault condition.

      CARB and auto manufacturers, yeah totally. If it starts out in CA, it might as well be national for exactly the reason you suggest.

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