Alternator light on

Sean Mobile Technician Australia Posted   Latest  
2007 Mercedes-Benz ML320 CDI 3.0L (642.940) 7-spd (722.9)
Battery Light Coming On After A Few Seconds

Hi all I've got a customers ML in at the moment for alternator light on. I have replaced regulator on the alternator with a genuine Valeo regulator. It runs up fine on the test bench and is charging on then vehicle at 14.20V this is a lin bus alternator. Dose's anyone have a wave pattern for this vehicle? or can anyone steer me in the right direction. I have replace glow plugs on the vehicle as they were shorting to ground and are also controlled by the lin bus,According to Auto Data's diagram lin bus only runs glow plugs,alternator and then runs to the ecu where the signal is sent via can bus to the cluster. I should also mention there is no codes stored on any control modules. thanks in Advance 

Mihail Mechanic

Did you scope the LIN bus? I would scope it first to see if there is any communication on it at all. Scope it connected and then disconnected from the alternator to see if there is any change. I am not familiar with the regulator that you have replaced but don’t imagine the alternator communication module to be built inside the regulator. You also need to scope the alternator output current…

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Ray Diagnostician

Do a full scan and post the codes related to the alternator and to the LIN bus

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Victor Owner/Technician

You need to check amperage output with an amp clamp. Voltage says nothing without amperage.

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Mohammad Owner/Technician

Just a couple of questions/thoughts...: 1- What was the initial problem with the car? The same, meaning charging but the light was on? 2- When you say running up fine on the test bench, are you in possession of any test equipment to supply LIN signal at the right Protocol to see if alternator reacts to different voltage setting and if the Protocol matches the original regulator's? 3- Any…

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Sean Mobile Technician

Thank you to everyone for the input. I've been having troubles with my laptop so i wasn't able to scope and patterns out with it. I have however resolved the issue on the vehicle, solution was to replace the aux battery on the vehicle.

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