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Do I have to buy this in order to get all the PIDs and the full instruction set for communicating with the car's obd ii interface via an ELM327? I tried looking for some kind of api for the ELM327 connector, but couldn't find any documentation besides the actual chip's schematics.
The standards linked above seem to provide the instruction set for all current obd2 protocols, can anyone confirm this?
If you're looking for the OBD2 pin-out on the vehicles end (female) then it the interface type and pin population will vary from vehicle make to vehicle make. In order to tell you'll have to start by locating the OBD-II Connector.
I'm going to assume since you're asking about this you know where to find this connector
The connector has metallic contacts in most of the pin-outs, with two rows of eight pin-outs each. You will have to make a close inspection of this pin-out configuration and from here you should be able to verify the protocol being used by this vehicle. There are three communication protocols
SAE J1850 VPW (Variable Pulse Modulation): Used in most General Motors vehicles and light trucks. Look for metallic contacts populating pins #2, #4, #5 and #16. Pin-out #10 should be empty.
SAE J1850 PWM (Pulse Width Modulation): Used in Ford vehicles. Check for metallic contacts in pin #2, #4, #5, #10 and #16.
ISO 9141-2 Used in Chrysler vehicles and most imports. Populated pins should include #4, #5, #7, #15 and #16.
NOTE: Variations do exist among certain models that are manufactured and branded as American, but are actually derivatives of German or Asian imports, for example. In this case, the vehicle might follow the ISO 9141-2 standard.
Once you've identified the Communication Protocol you will be able to determine much more about how the vehicle communicates to the mechanic.
The (original) ELM327 command is documented by ELM ELECTRONICS. Note that the wide-spread clones do not support the full command set.
Beyond that, the meaning of the actual PIDs, MIDs, TIDs, including the scaling of values and units is contained in SAE1979 and SAE1979DA, with 2014 being the last revision of both.
While you may find some of this material on Wikipedia and other sites, if you are serious about writing an own ScanTool, then you sooner or later really want to buy the standard documents, since they're the definite authority. You can mostly get away with SAE1979 and SAE1979DA which are about 75$ each.
