Charging issue
MBWorld Fanatic!
Joined: Aug 2014
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S500
what age? the later facelift ones like to do this...
I know of a "competent" indy garage with full merc diagnostics and 30 years history only working on Mercs, that battled this fun... Nothing comes up as wrong, replaced everything and the light is still on. Its a very common light on the later post 2010 cars - almost as if its a software enabled excuse to take 500 bucks out your wallet, with no ill effects actually in existence - a feature that is common in all later Mercs models
stick a volt meter on the battery.... should have something like 12.5v, start the car wait 3 mins and do the same should have 14.4v, if you have anything less than 13.9v you need to get it checked out.....
if you search youtube you should find the volt meter in hidden instrument cluster menu
I know of a "competent" indy garage with full merc diagnostics and 30 years history only working on Mercs, that battled this fun... Nothing comes up as wrong, replaced everything and the light is still on. Its a very common light on the later post 2010 cars - almost as if its a software enabled excuse to take 500 bucks out your wallet, with no ill effects actually in existence - a feature that is common in all later Mercs models
stick a volt meter on the battery.... should have something like 12.5v, start the car wait 3 mins and do the same should have 14.4v, if you have anything less than 13.9v you need to get it checked out.....
if you search youtube you should find the volt meter in hidden instrument cluster menu
MBWorld Fanatic!
Joined: Oct 2010
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From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
If the light connection is still like this it is very likely the alternator is bad as the light only cares about the voltage between the battery and what the alternator produces.
What comes to voltage at the battery it may not be higher than 12.8 V when on idle or driving without pulling lots of load from it especially if your car has the “smart charging” program. I have not measured in my S-class but in me E-class I can look at the voltages in the engineering menu while driving and I see higher than 12.8 V only when decelerating either with engine braking or by using brakes. Or for some reason when I turn the fog light ON voltage jumps up to 14.5V.
Easy check at battery is to check voltage when engine is not running. You should get just slightly higher than 12V. If with engine running you get anything higher it means alternator is working as the higher than battery voltage can only come from the alternator. If light is still ON and alternator works then the light connection is something else than what I explained above.
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Joined: Jul 2016
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2018 S450 4Matic, 2020 GLE450 4Matic, 2010 S550 4Matic(sold), 2012 ML350 4Matic(sold)
I recently had a similar issue. The voltage regulator is a wear part and can be replaced separately.
I changed mine and all is well.
Certainly, test before you change. As the others said, your voltage should go up when the car is running if your alternator is good.
If your alternator does test good, it may not be the main battery. It could be a bad auxiliary battery.
Tom
I changed mine and all is well.
Certainly, test before you change. As the others said, your voltage should go up when the car is running if your alternator is good.
If your alternator does test good, it may not be the main battery. It could be a bad auxiliary battery.
Tom
