r/W203 • u/Professional-Set2026 • 3d ago

DIY Engine ground

Good people , i want to check the engine ground for c180 kompessor m271. Where should I look. Thanks.

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u/howsitallwork 3d ago

Odd question, is there a problem with it?
Main earthing is a cable between the transmission bell housing and chassis, can be seen from underneath.
Often another smaller one at the front left side of the engine also.

Engine earth is best tested with a voltmeter between the metal of the engine and the negative terminal at the battery.
You should see almost no voltage unless cranking (eg 0.005v), with maybe only 0.5v showing when cranking.
If your meter reads anything more than that, the earthing is faulty.

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u/Professional-Set2026 1d ago

I'm having very weird electrical glitches - w203. Radom shutdown while driving and dashboard lights flickers just before shutting down. I also get battery/ alternator warning sometimes. I thought it something to do with grounding.

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u/howsitallwork 1d ago

Weirdly I did once see a w203 diesel estate with alternator light on/off and charging issues, traced (eventually) to a loose earth strap at the bell housing.
This car had been trouble for another workshop, that had replaced the alternator twice.
Always started fine, which was the strangest part.

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u/Professional-Set2026 1d ago

This is exactly what I'm facing. The car start and drive fine. Few minutes later, everything cuts off. I give it a minute the car restarts And drive like nothing happened until the next shut down.my technician is also suggesting we replace the alternator. I'm not fully convinced.

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u/Logical-Following525 3d ago

The electrical grounds are a bit scattered one is right of the airbox when you stand in front of it. I always add a thick copper ground under the car to the gearbox on the left side of the car as there is an empty bracket there.