The check engine light is trigged by the engine control module (ecm). When a malfunction with engine fuel management or emission occurs.
The ecm has to be scanned for fault codes. then the fault code has to be diagnosed
and a repaired.
You can choose to visit the dealer or a local mechanic to preform this service and they'll
charge to diagnose and scan the ecm.
Or you can visit your local parts store, like auto zone, and have then scan the ecm.
for free. but they will not be able to diagnose the issue. They will provide you with a fault code. Don't by any parts based on their recommendation. replacing parts will not repair
the problem it has to be diagnosed be a qualified Technician.
Sorry you have this impression, I did not recommend the dealer I said the dealer will charge you and I avoided that by saying check out the local parts store. As far as the causes I mentioned in the first sentence that it could be any of the emission and or the fuel management systems that the ecm controls. Never said it was an ecm at all.
I said the ecm has to be scanned because that's were the fault code is stored. that doesn't mean the ecm is bad nor have I indicated that.
The ecm has about 25 input and output sensors that supply it with information on how the engine is running. based on that information the ecm makes adjustments to maintain ideal running condition. No one can say whats wrong without havening the ecm scanned. It could be any one of those sensors, a vacuum leak, loose fuel filler cap.(assumptions).
I don't recommend the dealer or any one else, I recommended to have the fault codes pulled. I or someone else can help you understand what might be associated with the cost only when we have fault codes, and have them diagnosed.
When I replied to your question I wanted to give you a back ground on how the check engine light comes on, and what trigger's it. If I over explained I am sorry again.