Writing your approved tune (and reverting to stock)

Your order page shows the SHA-256 hash of the approved file. If your tool or OS can show a file hash, compare it — the file you write should be byte-for-byte the file the tuner approved.

Read the delivery notes before connecting anything. If the tuner left instructions (fuel, settling behavior, anything to check), they outrank the generic steps below.

Battery maintainer on, ignition on, engine off, accessories off, doors closed, key untouched for the duration.

Writes are less forgiving than reads: where an interrupted read costs you a retry, an interrupted write can leave the ECU in a state that needs recovery before the car runs again. The boring preparation is the whole game.

In your tool, select the same ECU you read, choose the write/programming function, and supply the approved file. The tool handles checksums and verification as part of its write procedure — let it finish completely, including any after-write verification pass it runs.

Do not touch the car or the laptop until the tool reports success. Writing typically takes as long as reading did, sometimes longer.

If the write fails or is interrupted: do not turn the ignition off, do not unplug anything, do not retry blindly. Follow your tool’s recovery procedure first; if you are unsure, stop and contact support with the tool’s exact messages.

After a successful write, switch the ignition off for half a minute, then start the engine. Expect a normal idle; some cars need a few seconds longer on the first crank while learned values settle.

Drive gently until the engine is fully warm before asking for full load. Listen and feel: anything unusual — rough running, warning lights, unexpected noises — means back off and get in touch rather than pushing on.

Your original file is stored immutably with its hash from the moment you uploaded it. Revert-to-stock is the same write procedure with that original file — available from your order whenever you want the factory calibration back.

Reverting before a dealer visit or an inspection is common and entirely up to you; the point of keeping the original byte-exact is that the way back is always known.