DIY updated my PCM/Dash software to improve first gear jerking and AC performance out of warranty using MDARS and VXDIAG.

Technical Disclaimer: First, a disclaimer, this is all at your own risk, and Mazda officially does not recommend doing this unless you run an auto repair shop.

You will need:

• J2534 Interface (I used a budget Chinese device costing less than $100 (VXDiag VCX NANO for Ford IDS 2-in-1 USB version (vxdiag.com)), but you can also opt for the official Mazda device which costs up to $2400).
• MDARS Subscription from Mazda (72 hours for $50) - Welcome to Mazda Service Info.
• A battery power supply, as you will keep the key in the "on" position with the engine off (Mazda's official recommendation is 15-20A, ideally using a charger that provides steady voltage to minimize fluctuations).

I followed this guide on the CX-90 website: DIY updates with MDARS | Mazda CX-90 Forum (cx90forum.com), but I would like to clarify a few things:

• Mazda only recommends updating the software when following the directive of a TSB or other advisory. Updating every module randomly can cause issues. For example: MC-10206943-0001.pdf (nhtsa.gov). I did not update the BCM module due to potential issues and uncertainties.

• When setting up the Chinese J2534, I used the software provided by vxdiag.com: Do not install Mazda or Ford-specific software; only install the J2534 passthru driver. I spent several hours troubleshooting due to software conflicts that interfered with the interface.

• A "smart charger" with variable charging rates can cause the update to fail. Using a "dumb charger" with a steady voltage is the safest way to proceed.

Finally, I would recommend that most people go to the dealership instead of doing this themselves.