louiscrystal1
Mercedes C Klasse Diesel Battery Alarm Problem Solved
Summary of the thread
A 2003 Mercedes C Klasse Diesel had an issue with the additional battery alarm. The problem was identified as a weak auxiliary battery, which was confirmed by a shop. Replacing the auxiliary battery resolved the alarm issue. Checking the quiescent current draw and performing a load test were suggested as diagnostic steps to identify potential parasitic drains or battery weaknesses.
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4 comment(s)
louiscrystal1 (community.author)
Thanks for the quick reply. Can you explain how to check the quiescent current draw and what values would signal a problem? I know about load tests, but I'm less familiar with quiescent current diagnostics.
miasteel2
To check quiescent current, use a multimeter in series with the battery's negative terminal, making sure all systems are 'asleep'. If the current draw is much higher than the manufacturer's spec (usually milliamps), there might be a parasitic drain. Given your symptoms and error codes, I'd still suggest a proper diagnosis from a technician. The repair cost seems fair for a battery and diagnostics.
louiscrystal1 (community.author)
I appreciate the thorough guidance. I took the car to a shop, and they confirmed the auxiliary battery was bad. Replacing it fixed the alarm issue, just as you thought. Thanks again for the help.
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MERCEDES
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CKLASSE
miasteel2
I had a similar issue with my old BMW 3 Series. It turned out to be a weak car battery. The IBS flagged low voltage, which disabled some features, including the alarm. Have you done a load test on the battery? A voltage reading alone might not tell you enough. Also, check the quiescent current draw.