Does Action Replay DSi Work on Firmware 1.4+?

No. Nintendo's 1.4.0 (and later 1.4.1–1.4.5) updates patched the exploit the Action Replay DSi cartridge used to launch its menu. The cartridge will show a black screen or "An error has occurred" on any DSi/3DS running firmware ≥ 1.4.

Options (All Carry Risk)

• Downgrade firmware – requires a hardmod (NAND soldering) or a second already-hacked DSi/3DS. High brick risk.
• Install custom firmware (TWiLight Menu++, Unlaunch, HiyaCFW) – runs homebrew, cheats, and ROMs from SD card. Works on latest firmware. Recommended path.
• Use a flashcart compatible with 1.4.5 (e.g., R4i Gold 3DS Plus, Ace3DS X) – runs Action Replay .cht files via TWiLight Menu++.

Legal/ToS note: Custom firmware and flashcarts violate Nintendo's Terms; online play may be banned. Offline single-player is generally safe.