Electric steering swap CANbus wiring, Subaru STi

Hello! I’m taking on the project of swapping a 2019 Subaru WRX electric steering rack into my 2018 STi. The rack only requires a 12v power from the battery terminal and chassis ground. In a smaller connector there is a 12v switched power and CAN Hi and CAN Lo wires. These would typically plug into the WRX chassis harness. I have seen another person do this swap by tapping into the CAN Hi/Lo wires at or near the OBD port I believe. Based on my access around the obd port and under the dash and reviewing the service manual diagrams I believe I would be able to tap into the BIU’s CAN wires. Im not too sure if that will work since i’m pretty sure it isn’t in the main CAN line, instead in the branch line (not sure if that matters). Second, on the BIU there is 4 connectors, CAN is in “i84” I marked what I believe are the correct wires to splice into. There is another set of CAN Hi/Lo labeled DIAG just above the red mark. Would splicing into the “Driving system CAN communication circuit 2” Hi/Lo wires be correct?

hi Jack,

Interesting problem.

From that diagram it looks like the EPAS module is on the powertrain bus so you would need to tap in to that rather than the chassis CAN bus.

Depending on how its configured by the OEM you may also need to flash a config file with the address of the EPAS module to allow it to communicate. Do you have .dbc files of the '18 and 19' to explore the differences and are you able to see what activity is on the bus with a CAN sniffer?

Hopefully its plug and play and the EPAS module can take whatever it needs off the bus.

Generally OEM's keep things locked down in terms of CAN to comply with UNECE 155 & 156 so it can make projects like this difficult. That being said it should be possible with earlier MY's and some OEM's are much slower to react to regulatory changes.

From what I’ve heard, with the CAN wires connected it is a plug and play swap. Do you know where the powertrain bus is / where could I tap into it? I was looking at more diagrams and saw I could splice into the CAN from connector B136, with CAN Hi-pin 17, Lo-pin 28 into the ECU. I believe that would be considered the main line. I don’t have .dbc files or a CAN sniffer, was hoping it would be a simple splice and install. Unlike the 15-18 WRX electric rack with a separate steering module, the 19-21 works just from the power and CAN communication. I attached another diagram with the Hi/Lo from connector B136. Any thoughts are appreciated