First you have to find the X11/4 diagnosis 8 pole locate right next the battery nearby firewall open cover press the button right next to the red LED light (engine at idle or with ignition on) for 2-4 seconds read how many time red LED light-up,if only light-up once =no malfunction stored more then one =malfunction stored in system press button again for 2-4 senonds if no more number stored the previously number will reappear.

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MB STARS Master Guild Technician,17 years MB tech
14 years independent shop owner