My Mercedes has a default note stating "Pre-safe Inactive and Check Engine Light On." The problem is that the transmission is not shifting from 2nd gear. I just tried detailing and washed the engine compartment light. Help is greatly appreciated. Thanks.
Since you said your Check Engine Light is on, the first thing I would recommend doing would be to have a qualified professional use an OBD2 scanner to pull the trouble code that is produced when your Check Engine Light comes on.
Depending on what the code is, the mechanic will have a lot better idea of how to begin the diagnosis of this issue. Without knowing the code it would be difficult to tell what is wrong with the vehicle.
Cleaning something will rarely fix a problem on an automobile, especially when it relates to electronic parts. If a bad sensor on your vehicle is causing the Check Engine Light to come on, I would recommend having the sensor replaced rather than cleaned. Get some help from a certified technician who can diagnose your Check Engine Light and fix your shifting problem accurately.
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