This is my attempt at writing something useful for people who want to pipe the CANBus signal from their ECU out to the stock OBDII port. I've only done this on the Link G4x, so this writeup will be specific to that platform, but I think it should apply to most, if not any ECU with CANBus capability.

Lets start by looking at the pinout for an OBDII port. Note that (probably obviously) there are pins reserved for CAN High and Low. Also note that there are pins resourced for 12 V and Ground. This means that if you don't need to run your own 12 V and Ground if you don't want to. In this scenario, I'm going to assume that whatever you're plugging into the factory plug will utilize the factory power/ground wiring.


First thing you're going to need to do is to get to your ECU and add wires to the CAN headers. For the Link I was able to use the plastic header with part number <!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}-->XARP-04V and the crimp pins I used were <!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}-->SXA-01T-P0.6. I'm not sure that the crimp pins are exactly what is called for in this application but I have used them for this project as well as making an I/O expansion cable for the G4x and that has been working without issue for months now.

I used white for CANH and green for CANL as those seem to be pretty standard colors for these signals.



Technically CAN is supposed to be a terminated twisted pair. I doubt it makes a big difference here, but feel free to twist your wires if you want to. I did twist mine, but did not add a termination resistor.

I ran the CAN subharness out of the ECU case towards the Denso 76 pin factory header. This puts it in a good direction to go to the factory OBDII port. Note that I ran 2 CAN harnesses here.


Next step is to go to the fuse box under the steering wheel. You'll find the OBDII port there which should be pretty easy to remove after pinching the tabs on the side. At this point you'll want to grab some OBDII crimp pins. I got a whole header complete with pins from Amazon for about $5.

I just grabbed it for the crimp pins, but in theory you could wire the entire harness into this and put it wherever you wanted.



Assuming you have the right crimping tool, you'll want to crimp pins onto CANH and CANL. I used a pretty generic crimping tool which I got with a DuPont connector kit and it worked fine.

For illustrative purposes, this is the orientation of the pins when they go into the plug.



Both wires go into the 3rd slot on the top and bottom of the plug respectively, refer to the diagram at the top of the post. The white piece here is a locking tab. There is a clip on the other side which will release it and allow you to add the pins to the plug.

I used a pick tool to push the wires into the connector.



At this point it's probably a good time to test everything before reinstalling. I'll cover that in the next post.

Assuming you've tested it or are just super confident in your ability, you can slap the OBDII connector back in the fuse box and you're good to go.


If you're using a bluetooth OBDII dongle, you may need to trim the fuse box cover panel a bit to get things to fit.

 

ETA - The "Car Scanner" app worked intermittently for me but often wouldn't be able to get data from the ECU, just the voltage reading from the OBDII adapter. I switched to the app "Torque" and have had no issues since then.

Setup in PCLink is pretty simple. Navigate to the CAN Setup Menu.

Once you're there you just need to change the Bit Rate to 500 kbits/s and select ISO 15765 on whichever CAN port you used. ETA - I think something caused these settings to work when I was messing around, but I tried yesterday and didn't see any data in the Car Scanner app despite it making successful connections to the BT dongle and ECU. Changing the Channel 1 to "Generic Dash" fixed this issue and is what I had set up for some initial testing.


I used a free app called "Car Scanner" to test this. I suppose I should also mention that I plugged a generic OBDII bluetooth dongle into the port. It's the cheapest one I could find on Amazon. Because OBDII is standardized to have CAN H/L on those specific pins mentioned above any OBDII capable device should work.

You should see reasonable values for IAT/CLT, RPM, etc...



Regardless, Car Scanner should be pretty good about picking up the proper bitrate (baud rate) and the ISO 15765 protocol. I also used RealDash with this setup (make sure to select OBDII and not Link in the app), but it didn't auto detect as well so I had to manually set the protocol in the app.

I've tested at 250 kbits and 500 and both seem to work fine. Initially I had some issues but that was due to some hacky wiring I had attempted on the bluetooth dongle.

I think this is probably the cheapest way to get ECU data without needing to have a laptop plugged into the ECU. Including the dongle and the OBDII plug I think this should be doable for most people for about $25 assuming you have some wiring and crimping tools. I haven't used this extensively yet, but have used it around town a couple times and it's a nice way to be able to monitor temps on the fly.

Keep in mind that not every ECU parameter is available on this. You might be able to accomplish that using custom data streams but I haven't dug into that. IAT, CLT, manifold pressure, timing advance, AFR, TPS and some others are available, but you might not find things like ethanol percentage, boost controller duty cycle, etc...

 

Just wanted to add another post/update. This has been working intermittently for me. I'm not sure if its the ECU or the app I'm using, but it seems like this will work, something will get out of sync between the two, and then I can't see data anymore.

I think it has something to do with the app remaining active between turning the car off and on. IE, the app still thinks it's connected but the ECU doesn't. I've played around with the settings on the Link and the Car Scanner app, but haven't found anything that has permanently fixed this issue.

 

I went on a roadtrip last weekend and really wanted to be able to monitor coolant temps on some of the longer hills. I ended up buying the app called Torque for $5. I had no issues the entire weekend with connectivity. I'd definitely recommend budgeting for that if you plan to go this route.