Automobiles of today are highly advanced pieces of machinery the first step in any automotive diagnosis is to connect a scan tool to check if any faults have been logged. Scan tools are needed to do basic settings on motors, modules and test various electrical components. The second step is to see if the factory has released any technical bulletins, a bulletin can quickly alert a person to a fix before a diagnosis is started. (you may be able to do this by searching on-line) If there are no bulletins found then a thorough diagnosis must be started. A test drive can show the condition of the car while it is being driven and help the diagnosis. If all else fails then the vehicle will need to be taken to a reputable technician. Preferably one who has experience with your make and model.
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