How to fix my Ac/heat? Will not come on...

Hello, the service engine light may or may not be related to the ventilation system not coming on. It is impossible to know without performing needed testing for the engine light. As a result, you may have two separate concerns - one for the engine light and likely mileage meter concern, and a separate one for the ventilation system. You could possibly also have a low system voltage issue affecting all components, but that's a total guess. You'll need some professional assistance to evaluate your vehicle and the concerns. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops