* Battery disconnection: During a paint job, the battery might be disconnected to prevent damage from sparks or overspray. Disconnecting and reconnecting the battery can sometimes trigger the light because the car's computer needs to reset various systems. This is the most common cause.
* Work near sensors: If mechanics or painters accidentally bumped or damaged a sensor (like an oxygen sensor, mass airflow sensor, or other emission-related sensor) while working on the car, this could trigger the light. This is less likely but possible if work was done near the engine bay.
* Loose gas cap: While less directly related to the painting, a loose or improperly tightened gas cap might have been overlooked during the process, leading to a code related to the emissions system.
* Pre-existing issue: The problem might have existed before the paint job, and the light just happened to come on afterward. The painting was coincidental.
* Software Glitch: In rare cases, a software glitch related to the car's computer system might manifest after the battery disconnection.
In short: The paint job didn't cause the light. Something else happened during the time the car was in the shop. You should have the car scanned with an OBD-II code reader to determine the specific trouble code causing the light to illuminate. This will pinpoint the actual problem.
