How long does it take for the check engine light to go out after repairs?

Hello, if you do not have a diagnostic tool present to "clear codes", you could disconnect the battery and let it sit for 10 minutes or so and reconnect it. If the light comes back on right away, you have a "hard fault" meaning a problem is actively still occurring. If not, drive it for a period of time to complete a "drive cycle" to ensure your problem is solved.