Is the mechanic making a assumption that it is the secondary air injection motor and charging me$490 for the repair. And what do I do if that isn't the problem.

Hello, it's honesty all about the relationship between the repair shop and the client. And in California, you have specific rights as to what is done, described, authorized and the transparency of what is being suggested and why. If you have questions, engage the management of the shop you are working with. You can alternatively find a RepairPal Certified shop near you by checking this link: https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.