Mercedes W212 battery light on

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Sean123a

New Member
Joined
Nov 18, 2019
Messages
8
Location
Surrey
Car
W212
Hi I’m new to hear , and I need some help please , so I have a 2010 w212 350 cdi , so the battery light came on so I managed to get the car home . The next morning I started it and went to a local garage and they tested the battery, and it was 10v so I went back home and as I got to my street all warning lights came on , so garage said it was an alternator, so I have changed the alternator today , but started the car and after a couple of minutes..... battery light on again and same thing happend , getting a new battery tomorrow so hopefully it’s that ,,,, but does anyone on hear know of any thing else this can be if it’s not the battery?? Thanks in advance
 
You may have changed the alternator prematurely. At 10v your battery was drained and low voltage will cause error messages and other faults. Did the garage check to see if the alternator was putting any charge into the battery? Hopefully a new battery will cure the problem.

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Thanks for the reply the alternator wasn’t putting enough out so I was told , so would of maybe cause the battery to fail , I will find out in the morning when the new Agm battery is fitted , thanks again
 
If the new battery sorts this out you'll need to report that to the garage that advised a new alternator.
 
Yes I will thanks for the reply, would you know of anything else it could be ie fuses if the new battery doesn’t sort it ??
 
Hi Sean,originally replied on wrong thread-I would imagine the recent cold spell has put paid to your battery(if the original then in it's 10th year so about right I would say),hopefully a new battery solves the problem.
 
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Hello again so I have replaced the battery this morning drove for about 10 miles , and noticed the heating wasn’t blowing very fast , 5 minutes later the battery light came on again ??? PLEASE HELP !!!!!!!!
 
You need a proper car electrician to find the cause.

If you don’t have the knowledge yourself, you are guessing in the dark.

If the new battery has died, you have a serious fault drawing it

Or the alternator is not connected properly (dodgy belt, broken circuit)

Patience and logical elimination is the way forward
 
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Just barely got the car home ??
 
Let’s get some basic facts to help eliminate some possible causes:

1) did the garage replaced the alternator with a new/reconditioned/used alternator?
2) does it comes with a warranty?
3) do you know the make, model and capacity?
4) did the garage give the old alternator and did you keep it?
5) did replace the battery with a brand new battery or a used battery.
6) what is the make, model and capacity of the replacement battery?
 
Ok thanks for the reply, I brought a new alternator ,, wai 180 amp witch matched the reg ,I have the old alternator.. brand new boch 12v 800 amp battery , I’m not that good at putting words on paper so please excuse my way with words
 
Ok thanks for the reply, I brought a new alternator ,, wai 180 amp witch matched the reg ,I have the old alternator.. brand new boch 12v 800 amp battery , I’m not that good at putting words on paper so please excuse my way with words
Great - getting a new alternator and battery allows us to eliminate these for now, although one one o the other could be faulty, however unlikely.

Do you know if the garage fitted a new belt when they installed the new alternator? Can check if the belt is tight with the engine off? Can hear any slipping noises wth the engine idling?
 
The belt is tight and no noises coming from there ??
Thanks
Ok, it has been a while since I had to deal with the battery light coming on - from memory there isn’t sufficient voltage which means that either the alternator isn’t kicking out enough of a voltage or the battery voltage warning circuit is faulty.

Best to check the voltage across the batttery with a voltmeter with engine off and with the engine idling. If you don’t have a voltmeter you start the car and turn on the lights, fog lamps and high beam. Put the cabin fan on at maximum and turn on the rear demister. Now get to look at the brightness of the headlights as you rev up the engine from idle to around 2500 rpm. If the lights do not brighten up your alternator may not be working properly.

Alternatively get one of those ciggerate lighter usb charger with a built in voltage display.
 

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