the check engine light only comes on when the onboard computer detects a fault in either the engine management system, transmission, or emission control system. Faults can range from vacuum leak, engine misfire, transmission problem, emission control leak, one of dozens of engine or transmission sensors, or even internal engine or transmission failure. There are over 500 fault codes that can cause the check engine light to come on. And not every one has symptoms you can feel or see or hear.
The only way to determine which of the over 500 faults is responsible is to have the onboard computer read with a diagnostic scanner. once this is done and the fault code retreived then pinpoint diagnosis can be done and repair done.
without knowing which of the over 500 faults is responsible, it is simply impossible, as well as irresponsible for anyone to guess at to which one is responsible for the check light coming on.
So you will need to have a shop use a scan tool to read the computer for the stored fault codes and go from there in diagnosing and repair
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