VA STI ROM & Logic Changes between versions

Hey Guys,

So I've been checking out a few different open source ROM options and one thing I've noticed is that for some of the patched ROMs available out there, some people seem to be taking ROMs with IDs from earlier generation cars (eg: base ROM from a 2016 car), relabeling it and then flashing it into a later generation car (eg: a 2020 car).

It looks like Cobb previously had some tech bulletin's up about "changes" between these generations of cars here:

https://cobbtuning.atlassian.net/wiki/spaces/PRS/pages/62914580/Tech+Bulletin+-+2017+WRX+STI+-+Subaru+Logic+and+OTS+Calibration+Changes

https://cobbtuning.atlassian.net/wiki/spaces/PRS/pages/161447950/Tech+Bulletin+-+2018+WRX+STI+-+Subaru+Logic+and+OTS+Calibration+Changes

But its not clear to me whether one would expect that these types of changes between generations of cars would be:

a) Configuration changes (eg: same tables between generations but starting values are modified/tuned differently between cars)

b) Software changes (eg: hardware remains the same, but there may be new tables interacting in new ways past just config/tune changes)

c) Software & hardware changes (eg: software has changed in conjunction with hardware changes)

I would assume that If changes were made between generations of cars that were only a) or b), theoretically it would be possible to reflash an older car w. newer ROM versions or vice versa and it should just "work" as you are just loading up a new (or old) software version kind of like how you can change the version of your operating system on your computer and different versions work on the same hardware?

Perhaps this is getting too into the weeds of reverse engineering that HPA seems to steer away from but seems relevant to ask non the less.

Hello, I wrote those documents you linked. Each item indicates whether it's logic/strategy and values, or just value changes, but much of it is both. The pinout didn't change much across those years in terms of physical changes.

COBB does not swap ROMs between years because they maintain compliance, but 15-16 are essentially the same, 17 was a big change (hence the document to help tuners understand), 18 small changes except Subaru added a CAN gateway, 18 RA, 19-21 STI have significant emissions and readiness test changes because those are tier 3 vehicles.

I'll just say if you put the wrong ROM on an ECU sometimes it is not recoverable and the vehicle will be inoperable until the ECU is repaired, or replaced + the immobilizer is reprogrammed by a dealership. COBB does offer repair services for people who break their ECU, but recovery is not always possible.

Ok awesome thanks for clarifying that Mike

You're welcome.

When only values in existing tables are updated I mention changes to "values" and then if the way a system or subsystem works changes, tables are added/subtracted, or the way they interact or function is altered, then I mention a change in "strategy" or "logic". The terms aren't necessarily used in the same manner by everyone, but hopefully that helps decipher info like this.