I got a 2006 s40 t5 6 spd, bad engine. (first p1 s40II) I plugged it to my dash I noticed that the car doesn't need ECM pin decoded. if I decoded the CEM. If I was to ditch the ECM and use an aftermarket source what would and would not work?

I was thinking of something cool maybe even switchable. between oem and aftermarket. like "normal" mode "track" mode. Most standalones are CAN compatible with most oem brands

The car was given to me, I'm more familiar with P2's. pretty sure these also use Bosch ecus. just really tinkering as I rebuild the engine.

if I was to ditch the ECM and use an aftermarket source what would and would not work?

would be looking at using Haltech, MAXX, LINK.

Any valuable info and ideas or anyone.