I used to work in the engine control group at Chrysler. Vehicles have many interconnected communication busses, and much of the software is secret so hackers and car thieves can't mess around.
I once worked on a project were we connected fleet control boards to the canbus of the vehicles. Some data was easy to probe, such as the RPM meter, but other data was much harder to probe, and not standardized at all. The implementation of a generic solution ended up being a mess, I believe in some cases the signal was sampled directly from the analog signal sent to dashboard indicators.
Top Comments