Question about 2003 Mercedes-Benz C-Class

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2003 Mercedes C320 Coupe\r\nBattery/Alternator

2003 Mercedes C320 Coupe Battery/Alternator visit workshop malfunction message

I was driving home last week and my car died due to a bad alternator. My headlights shut off, abs deactivated and the car went into a limp mode state. I pulled the vehicle into the nearest service station and had it towed to my mechanic. My mechanic replaced the alternator and the battery. The car drives great but we were unable to get the battery/alternator warning visit workshop message to go away. We tested the battery and alternator, and everything seems to be charging and working. I even left the vehicle for 3 days and it started right up. What could be causing this warning to stay on? Is their something I can try to clear the warning? My mechanics diagnostics do not show any error codes at all. What i thought was a minor problem is turning into an expensive one.

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There is a TSB (technical service bulletin) affecting these models for faulty voltage regulator on the alternator. This should be checked, as well the alternator diode output should be checked with an oscilloscope to ensure no bad diodes, even in a new alternator. Also codes can be cleared in one of two ways, with a global obd II scanner or with the Mercedes scanner (dlc located in engine compartment right rear). also all wiring and connections should be checked for high resistance. hope this will help with your problem otherwise bring it to certified Mercedes dealer and have it checked / cleared. good luck

Posted on Feb 05, 2010

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If you have a warning light then you need the appropriate diagnostic tool connected to this vehicle.The right equipment connected to this vehicle should clear this warning, I suggest you contact a proper merc dealer/repairer. There is a cable called EL 327 which you could buy off ebay for around 30 usd and I have personally tested it and I have referred more than 50 clients here and all have succeeded in using this tool.Now it is up to you to decide if you want to pay for this service or else get yourself this diagnostic tool which would be quite handy in future.Another advice is to ask if this would work on merc.
Vehicles I tested are : vaiuxhall, opel, nissan, ford ( Uk), Now I do not have a list of vehicles for my clients but they all suceeded.Yours is a post 1997 and thus uses OBD 2 technology.Now this warning light came up as there was a fault on the car and even though you have fixed this problem, the computer memory of the car still think there is a fault and can only be corrected using a diagnostic tool.Hope this helps.

Posted on Feb 05, 2010


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There is also a reset procedure that you can use that involves disconnecting the battery, turning the ignition to position 1 several times and then reconnecting the battery. That procedure can be found with a google search.

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