ODB2 Plug / CAN

[FoxSTI]

Hello guys, I have asked a similar question in the past before having an understanding of the difference between CAN and OBD2. With that said, my C125 has been using the physical ODB2 plug and the same protocol to display and log some information.

Here are my questions and challenges :

1 - I want to free up my ODB2 plug for another device.
2 - Can I splice wire to the back to the ODB2 connector in my car and still use the same protocol for now.
3- In the future, should I be able to use the same wires I taped into and just send a CAN request from the Dash, or a mixture or CAN and OBD2?

The ultimate short term goal is to free the ODB2 port / Long term goal is to get car info via CAN.

Thank you

[adrian]

The Dash only uses CAN OBD (not one of the other protocols) so in your case they are the same thing. You can simply splice the CAN wires into the back of the OBD2 plug and then get information either directly from the vehicle CAN bus (if you reverse engineering the messaging structure) or via OBD2 request messages (what you are doing now).

[FoxSTI]

Adrian thank you.
Just for my information, what other CAN protocols are there? And are these available to other dash models?
Or are all the same?

[adrian]

Are you talking about CAN protocols or OBD2 protocols?

There are a few CAN protocols, OBD, J1939, CANOpen and so on that work with all of our current dashes.

The other OBD2 protocols include K-Line and some other more manufacturer specific ones which none of our Dashes work with.

[FoxSTI]

Thank you. So I am able to figure out CAN data for my car, the dash will always have to be configured to"ODB-II Transmit" parameter on the CAN Communications setup window /tab?

[adrian]

You can think the vehicle CAN and OBD CAN giving you the same information in slightly different ways. The OBD is request based, so if you want Engine Speed you have to send a message to the ECU saying you want Engine Speed and it will send it back.

OBD is a standard that car manufacturers have to implement (since about 2007) so it is easy to get certain diagnostic information from the vehicle as all cars have to do it the same way.

The actual vehicle CAN will often have the exact same information sent continuously on the bus so you don't have to send a request message. It will normally be sent at a much higher rate than the OBD messaging so it is a lot more useful (especially for engine and vehicle speed channels). However there is no requirement to send this information in any particular way so car companies do what they want. They will also never release this information to the public, hence the requirement to reverse engineer the bus.

You will only need to keep the OBD-II Transmit message in the comms setup if you want to receive information this way. Otherwise if you receive the channels directly you just put in standard receive templates to match.

As an example, lets say you get the information to read Engine RPM and Wheel Speeds directly from the CAN but can't find any information on Ignition Advance. You would put in standard receive templates to read the Engine RPM and Wheel Speed channels but would leave the OBD-II transmit message in as well so you can continue to get Ignition Advance.

If there is nothing in the OBD-II transmit you can't get directly from the bus then you can remove it.

[FoxSTI]

Is this what you mean in your example?
Adrian, I know this may be too much to ask, but do you have a setup the in CAN based for any car that I can look at as an example? I would go along way.

[adrian]

Yes that is correct. You would use a receive message template for all of the channels you are receiving directly from the CAN.

Below is an image showing the setup of a Dash that uses OBD for most of the channels but also gets Wheel Speeds directly from the CAN bus.