First, breathe: the flash routine in these ECUs lives in a protected region that a normal failed write doesn't touch. A 'bricked' EJ ECU is almost always just an ECU holding a half-written map — recoverable from your driveway with the same cable that got you here. This is also why the stock-ROM backup guide came first.
Step 1 — Diagnose what actually happened. Write failed with an error but car still starts: the old ROM may still be intact — read the ECU and check. Car cranks but won't start after a 'successful' flash: likely a bad or wrong ROM, not a bad write. No communication at all: start with physical basics — cable seated, fuses, battery voltage.
Step 2 — Restore the basics before heroics: battery on a charger, ignition accessories off, laptop on wall power, direct USB. Half of failed writes trace back to voltage sag or USB dropout, and retrying with the same weak setup fails the same way.
Step 3 — Attempt a normal write of your verified STOCK ROM backup. In many failed-flash cases the ECU still communicates normally and simply accepts the rewrite. If it completes: key cycle, start, confirm, and go figure out what was wrong with the ROM you tried before.
Step 4 — If ECUFlash can't establish normal communication, use the flash recovery mode. EJ-era ECUs can be forced into their bootloader for recovery; the exact entry method varies by generation (the ECUFlash documentation and community wikis document each — for many cars it involves a specific test-mode connector state during the attempt). Follow the documented procedure for YOUR generation precisely.
Step 5 — In recovery mode, write the stock ROM, and treat it as the most delicate write of your life: absolute stillness until success. Key cycle and start.
Step 6 — After any recovery: read the ECU, verify the CAL ID, then do a normal write of your stock ROM again so you know the ECU is in a fully known state. Log a drive and check for oddities before re-attempting any tune.
Step 7 — Post-mortem in your notes: what failed and why. Weak battery? Bad ROM source? USB hub? Recovery you learned from once is education; needing it twice for the same reason is a habit.
The genuinely rare worst case — an ECU that no procedure revives — is a used-ECU-plus-reflash situation, not a dead car forever. But in years of community history, nearly every 'bricked' thread ends with the recovery mode working.
Tuning changes engine behavior. Numbers here are typical, not guaranteed — your fuel, climate, and hardware matter, and a professional calibration for your specific car always beats a generic map.