Why does my Audi A5's check engine light keep turning on?

I recently purchased a pre-owned Audi A5 and have been experiencing problems with the check engine light turning on for seemingly no reason. I took it to a mechanic and they couldn't find any issues. What could be causing this and how can I fix it?

The check engine light could be turning on due to a faulty oxygen sensor. If the sensor is not functioning properly, it could be sending incorrect data to the car's computer and causing the light to turn on. It's best to have it checked and replaced by a certified mechanic.

Another possible reason for the check engine light could be a loose gas cap. If the gas cap is not securely tightened, it can cause the light to turn on. Check to make sure the cap is tight and replace it if necessary.

If the check engine light is flashing, it could indicate a more serious issue with the car's engine. It's best to pull over and have it towed to a mechanic for further diagnosis and repairs.