Need to free up my ODB2 port..

[FoxSTI]

I need to free up my ODB2 port. Unfortunately using a spitter does not work on the second device.
My vehicle is running an OEM ECU, but being a modern vehicle I am sure it has CANBUS. Is it possible to connect the dash directly to the cars canbus and get the same information I am currently getting on the dash ?

(vehicle speed, rpm, coolant temp, intake temp etc).

Thank you

[adrian]

Unfortunately using a spitter does not work on the second device

What exactly do you mean by this? The dash is simply connected to the two CAN wires in the OBD-II port and there is no issue splitting these wires to other devices.

Just make up a little patch loom that has the male and female OBD plugs on it and then splice the two CAN wires out to the dash. Run wires straight through for all of the other pins and that way it doesn't matter what you other device needs all of the connections will be available and you can connect it directly into the patch loom.

You can read from the vehicle CAN bus directly but you will have to reverse engineer the messaging to get the information you need.

[FoxSTI]

You can read from the vehicle CAN bus directly but you will have to reverse engineer the messaging to get the information you need.

Whereas if I were to use a Motec ECU, I would the Motec ECU's CAN connection to get the info onto the dash, is this correct?

Maybe the ODB2 Splitter I have is broken. I will try again. So you are saying I could have to C127's read info from the car at the same time? (almost doesn't make sense since requests take time don't they?)

[the_bluester]

Yes, it should be possible to have multiple dashes or other devices on the BUS. It is just that, a BUS system, so the data lines are common to all devices plugged into it.

Race car so done differently but my setup will have the ECU, Dash, PDM and keypad (At least) all on the one CANBUS.

[FoxSTI]

I did some more research to educate myself on the CAN vs ODB2.
it theory I should be able to feed as many devices as I want via ODB2, and I also understand why I would need to come up with a way to "decode" the native CAN messages for my car. So the answer to my question would be to still connect to the Hi and Lo CAN wires (in similar fashion as ODB2), however use another protocol to capture the data I am seeking. In then end, its the same as using my OBD2 PID's - there is really no advance. Am I right?

[adrian]

The biggest difference between using OBD-II and directly reading from the CAN bus is the rate at which you get information. OBD is request based, so you have to send a request message to get a message back. The problem with this is that the ECU will only respond at a certain rate and it is usually pretty slow.

So for instance on my WRX if I plug in a dash requesting Engine RPM via the OBD protocol at 12.5Hz the ECU actually only responds at 6.6Hz. However, if I read directly from the CAN bus I can get Engine RPM at about 70Hz.

It really depends on what you are trying to do with the data. If you are simply using it to display to the driver then 6Hz is probably enough (just). If you are actually doing some proper data analysis then 6Hz really isn't even close to what you need.

[FoxSTI]

Adrian, I completely understand.
So if I wanted to subaru's CAN protocol, I would still phycially connect to the car's Hi and Lo CAN wires (probably the same ones found on the the ODB2 port) but as you mention I need to come up with a way to capture the data I am wanting to display and log.

Do you have any ideas or where I can start looking for this information?

[adrian]

Yes you will need a device to read the raw CAN values. We typically use CANCapture or CANalyzer which are both reasonably expensive but very powerful. You can probably find something that is a bit simpler but much cheaper on Ebay that would do what you want.

In terms of getting the CAN information it is unlikely anyone will simply give it to you. The car manufacturer certainly won't and reverse engineering is very time consuming so any company that has done it already is unlikely to give it away for free.

Unless you get lucky you will probably have to reverse engineer it yourself. The easiest way to start is to simply make some CAN logs with a device connected sending the OBD-II messages. The screen shot below shows the raw CAN messaging from my car with a dash transmitting the OBD-II messages. As you know what the structure of the OBD messages are, you can compare them to the other messages to try and find the channels you are after.

WRX CAN.png (60.31 KiB) Viewed 18782 times

[FoxSTI]

Are the CAN wires on the OBD2 port always sending information? Meaning, if I am ever able to figure something out, what would the physical connection from the car to the C125 be like?

[adrian]

Yes, almost always the CAN bus in the OBD port is just one of the standard vehicle buses so will have continuous traffic while the ignition is on. What information is on this bus is completely up to the vehicle manufacturer and it won't necessarily have everything you want.

Modern vehicles often have multiple separate CAN buses, so you might find that certain information isn't on the bus connected to the OBD port but is on another CAN bus.

The connection to the C125 will simply be the two CAN wires connected to pins 6 and 14 in the OBD connector.