There are many posts on this subject, but to sum it up there is a problem with the air pump for the catalytic converter. It pumps air to the converter so it heats up faster and doesn't pollute so much during cold starts.

My light came on for the same thing at 37K and it was an electrical problem. The relay module is usually the cause as they are cheap pieces of sheet in this car. Tell the mechanic to see if the pump itself is getting power and if not, 99% of the time its the relay module.