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2018 Subaru STi Can Mapping
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Post 2018 Subaru STi Can Mapping 
I had the chance to help a friend install a RCT into his 2018 Subaru STi this weekend, and wanted to pass along some lessons learned.

Unlike my 2015 WRX, the 2018 STi appears to require a different Can H/L tapping location. Originally we tried tapping Can H/L at the OBD port. This resulted in no can data. We spent hours diagnosing a wiring problem, thinking that we improperly tapped Can H/L. After half a day, I desperately called a friend with a 2015 STi and RCT. He suggested turning on the OBD presets.

Suddenly we had two can packets being received by the RCT. However, this is very very far from the typical can bus dump with thousands of packets and multiple IDs. Here is an example of what we were seeing:
Code:

[2024.0]: 3.0, 65.0, 17.0, 33.0, 0.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 4.0, 65.0, 12.0, 11.0, 166.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 3.0, 65.0, 17.0, 33.0, 0.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 4.0, 65.0, 12.0, 11.0, 166.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 3.0, 65.0, 17.0, 33.0, 0.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 4.0, 65.0, 12.0, 11.0, 190.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 3.0, 65.0, 17.0, 33.0, 0.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 4.0, 65.0, 12.0, 11.0, 190.0, 0.0, 0.0, 0.0,
[1882.0]: 3.0, 127.0, 1.0, 17.0, 0.0, 0.0, 0.0, 0.0,
[2024.0]: 3.0, 65.0, 17.0, 33.0, 0.0, 0.0, 0.0, 0.0,


We spent the rest of the night scratching our heads. This made no sense. We studied the wiring diagrams for the car and noticed the OBD ports only connection to Can H/L came directly from the BIU/BCM (body integrated unit/body control module). All of the can wires fed into two junctions, which then fed into the BIU/BCM, then the BIU/BCM was connected to the OBD port. The diagram for my car(15 WRX) was similar, but there were 2-3 devices also connected downstream of the BIU/BCM, on the OBD port side, that seemed like it would require info from the rest of the upstream devices. Our guess, the 2018 BIU/BCM was filtering the can bus packets, keeping them away from the OBD port.

To test our theory, we decided to tap into the Can H/L wires upstream of the BIU/BCMn hoping that we would find a fully exposed bus, rich with can packets. We decided on taping the Can H/L wires going into the multi function display. The MFD is the center display above the headunit, and displays information like pitch, steering, vdc data, etc( But data that we know requires can info).

And...it worked. The following day we were sorting through full can data.

We were able to find the following data by passive can sniffing:
Steering
Brake
Throttle
Coolant
Wheel speed (FL, FR, RL, RR)

We were able to request the following data by OBD:
RPM
Manifold Pressure
Barometric Pressure
and a host of other items.

There is a document attached that out list the specific OBD PIDs for the 18 STi.

*********
However, we seemed to be having an issue with requesting more than 3 OBD parameters simultaneously. I'm not sure what the issue is and we ran out of time to figure out what was going on.
*********

Ultimately, we had a pretty productive weekend. Our future goals are to find:
Dynamic Advanced Multiplier
AF Correction #1
AF Learning #1
Fine Learn Knock
Feedback Knock
Boost
Gear Position
AVCS
Ignition Timing

Attached, the RCT config. Remove the .zip suffix in the file name.
18 STi OBD PIDs : https://drive.google.com/open?id=1oixjo1-seiACdKxtrSoE8XBR5nmDoGtV

And of course thank you to Nathan (15 sti owner) and Brent Picasso for being a sounding board during the entire process. Love this community!

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Thanks for the detailed post. Great read!

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