Bad Alternator or Battery?
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MBWorld Fanatic!
Joined: Aug 2014
Posts: 1,060
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From: Montreal, QC
E55 AMG & C63 AMG
Bad Alternator or Battery?
Driving home tonight I got an orange battery light on the dash. Once home, I restarted the car and it went away, only to drive down the block and have it come back. Went through the Dyno Mode process to see Vehicle Data and got the following readings...
Car at idle:
I understand voltage should read 14.7. Car also seems to be pulling a lot of current at -52A. I'm wondering if this is the battery not holding the charge or the alternator not charging. Checked the belts and everything is nice and tight.
Any input it appreciated. Have a road trip planned in 2 days, so hoping battery is the fix...
Car at idle:
- UB: 11.6V
- IB: -52.0 A
I understand voltage should read 14.7. Car also seems to be pulling a lot of current at -52A. I'm wondering if this is the battery not holding the charge or the alternator not charging. Checked the belts and everything is nice and tight.
Any input it appreciated. Have a road trip planned in 2 days, so hoping battery is the fix...
Last edited by MTV10; Jun 4, 2019 at 11:43 PM.
MBWorld Fanatic!
Joined: Jul 2012
Posts: 1,556
Likes: 15
From: Canada
07 E63 + 07 CLK63CAB
How old is the battery, Try to charge the battery overnight voltage should be 12.5 to 12.7 unloaded
If you want to test the battery turn on the aux in the key and turn on the headlights heater and seat heaters for 2 or 3 min now check the voltage if it is below 12.0 the battery is toast
If battery checks out start the car the voltage should be 14.2-14.4volts
Could be the regulator inside of the alternator which causes some fuss, or if the battery is old ( 5-7 years ) also load test is also good at a battery shop
Or replace the alternator all together if the mileage of the car is over 100000 km
Hope this is helpful
But if you do put in a battery and call it a good day monitor the voltage when driving it should be 14.2 volts all the time
If you want to test the battery turn on the aux in the key and turn on the headlights heater and seat heaters for 2 or 3 min now check the voltage if it is below 12.0 the battery is toast
If battery checks out start the car the voltage should be 14.2-14.4volts
Could be the regulator inside of the alternator which causes some fuss, or if the battery is old ( 5-7 years ) also load test is also good at a battery shop
Or replace the alternator all together if the mileage of the car is over 100000 km
Hope this is helpful
But if you do put in a battery and call it a good day monitor the voltage when driving it should be 14.2 volts all the time
Super Member
Joined: Oct 2014
Posts: 701
Likes: 103
From: Ontario, Canada
2009 C63 AMG, 2010 C250 4Matic Sport
Voltage should definitely be above 13v when the car is running. Alternator or voltage regulator on the back of alternator has probably died.My case, it was the alternator entirely
Super Member
Joined: Dec 2012
Posts: 600
Likes: 6
From: Bay Area
2010 C63 P31 AMG
possibly alternator dying if not battery. Similar happened to me until it fully died and could not start car.
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From: Worldwide
2007 Mercedes E63 AMG
i had similar issue....i replaced the voltage regulator. it was 90 bucks? i'd have to check to be sure. very easy to replace from under the vehicle.
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Out Of Control!!
Joined: Apr 2019
Posts: 11,923
Likes: 6,775
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
not exactly witchcraft but....
The silent killer is the poor Engine-Chassis GND strap that glitched the snuts out of overheated electronics.
Just don't jump blindly to conclusion. This is the best German engineering - Go the extra mile when it is your own toy kit.
ECU can be in on voltage swings below 12.0. What do you ecpect: this is way more fun than a Toyota!
Last edited by CaliBenzDriver; Nov 26, 2023 at 12:29 AM.
