When you encounter issues with your Mercedes Benz ML350 it can quickly become a frustrating guessing game unless you can perform a proper diagnosis. As is the case with the majority of vehicles on the road today, the ML350 comes equipped with an onboard diagnostic system, known as OBD2, which will output specific error codes for specific points of failure within your ML350's electronic and mechanical systems. You can use an OBD2 scanner, available for purchase at most auto parts stores (or available to be used for on-site scanning for free at many auto parts stores) to scan your ML350's onboard diagnostic computer for error codes.
Determine the location of the OBD2 port on your ML350 by feeling around for it below your steering wheel at the top of the driver's side foot well. The diagnostic port will be marked with OBD and will be approximately two inches in width.
Plug the OBD2 code scanner into the diagnostic port, then turn on your ML350 so that the engine is idling. If you are having issues with your engine and cannot get it to idle, turn the ignition to the accessories position instead so that the vehicle's interior electronics are activated.
Let the code scanner scan for any error codes that will be sent as output by the diagnostic computer in your ML350 and take note of any codes that appear on the display of the code reader.
Bring the codes that were displayed to a licensed mechanic, auto parts store or Mercedes dealership to be decoded. All three of these resources will have books and computer records on hand that can tell you if the error code you received is, for example, indicating a failing sensor.
