They are basically the same engine but scaled up. I’ve read issues regarding the 2.5, but I find it rare and does not seem that much of a big deal to fix to me. You cannot go wrong with either, Skyactiv-Gs are very reliable, but Skyactiv-Ds are a different story…
The OEM oil is supplied by Total. You can use any other brand oil if it matches the required viscosity AND specifications.
4th gen. Mazda 3s (which firstly had the 7th gen Mazda infotainment) didn’t have a TCU unit in them up in EU models up until 2022. There’s a debug menu of the infotainment which shows if the TCU is present or not.
As it implies, there’s no functionality in the MyMazda app which depends on the TCU unit (remote start, remote lock/unlock, door state, tire pressure, etc.).
There’s no codes thrown on the dashboard of course as these cars came out of the factory like this, but firmwares differ for the infotainment system based on model, region, VIN ranges for facelifts, etc., so not sure how a car which should be having a TCU would handle the removal of it.
In Mazda 3s I believe it should be behind the dash, but not sure if the whole dashboard should be removed to access it and that would definitely introduce some rattles.
Personally I wouldn’t remove it if my car had it (have a 2019 gen 4 Mazda 3), there’s much common privacy destroying things which are more general than having a TCU in your car (like posting to reddit).
Those are just DTCs because of low/fluctuating voltage. They’ll go away after a few restarts. Get a new battery, OEM is crap