Red Battery / Visit Workshop
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Joined: Sep 2015
Posts: 57
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2005 Mercedes-Benz E500 W211
Red Battery / Visit Workshop
I just bought a 05 E500, it looks like the previous owner had a aux battery replaced at autozone and they put it in backwards. The negative terminal on the aux battery was completely fried. I replaced the aux battery but unfortunately the red battery/visit workshop message is still there. The vehicle drives fine, everything works as far as I can tell which I'm assuming means the alternator is good. If I let the car sit and not drive it for a day it still starts fine the next so I'm assuming there is not a battery drain. I think I probably need to replace the battery relay but I'm no Mercedes expert. What do you guys think?
Appreciate the help! I will update when the problem is resolved.
Appreciate the help! I will update when the problem is resolved.
Last edited by seawind; Sep 19, 2015 at 10:20 PM.
Thread Starter
Junior Member
Joined: Sep 2015
Posts: 57
Likes: 6
2005 Mercedes-Benz E500 W211
Unfortunately I don't have the equipment to read the faults but I think I might know a independent mechanic that could for me on Monday.
After sitting over night before starting the main battery is at 12.32 and the aux battery is at 12.36. At idle the main battery is at 14.20 and the aux battery is at 14.15.
If the main battery is detached the aux battery still powers all the lights so I'm assuming the wiring harness is fine.
I looked at the fuse chart but can't find a battery fuse. Is there one?
I think I found the aux battery relay on the passenger side if you are looking from the front of the car to the right of the air filter. It is a bit different then your typical car relay but if I'm testing it right I'm getting 0.05 ohm.
After sitting over night before starting the main battery is at 12.32 and the aux battery is at 12.36. At idle the main battery is at 14.20 and the aux battery is at 14.15.
If the main battery is detached the aux battery still powers all the lights so I'm assuming the wiring harness is fine.
I looked at the fuse chart but can't find a battery fuse. Is there one?
I think I found the aux battery relay on the passenger side if you are looking from the front of the car to the right of the air filter. It is a bit different then your typical car relay but if I'm testing it right I'm getting 0.05 ohm.
Last edited by seawind; Sep 20, 2015 at 06:50 PM.
Thread Starter
Junior Member
Joined: Sep 2015
Posts: 57
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2005 Mercedes-Benz E500 W211
Solved, bad battery control module. My family member has a similar 03 E500 so I swapped the battery control module in the trunk and the error has disappeared! Unfortunatly I have to give theirs back lol, battery control module ordered now I just got to wait a few days for it to come in...
Last edited by seawind; Sep 20, 2015 at 06:53 PM.
Thread Starter
Junior Member
Joined: Sep 2015
Posts: 57
Likes: 6
2005 Mercedes-Benz E500 W211
Don't you have to have Mercedes equipment to do that? I thought about going that route but I'm assuming when the aux battery was hooked up backwards it probably fried something in the module. I found a used module for $165 which is probably less then what Mercedes would charge me to flash it.
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Thread Starter
Junior Member
Joined: Sep 2015
Posts: 57
Likes: 6
2005 Mercedes-Benz E500 W211
Is 12.3 low after sitting over night? I'll check the battery again after I replace the battery control module, I know I checked it once and got 12.6 but I had probably just turned it off during troubleshooting. Thanks for the heads up!
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From: MA
2008 E350 4Matic, 2011 E350 4matic
A fully charged new battery at rest with no load is supposed to be 12.7 at 70 degrees. Voltage will be lower at lower temperatures. It's possible that it isn't fully charged. Also older batteries won't take a full charge but are still good, mine reads 11.9 right now, but then again, it's an 8 year old battery and in the winter it's as low as 11.5v. I believe the warning comes on when it hits 11 volts. Note that with the battery connected to the car, the voltage you're reading is not an open circuit no load reading.
Here's a state of charge chart:
http://modernsurvivalblog.com/altern...-charge-chart/
Here's a state of charge chart:
http://modernsurvivalblog.com/altern...-charge-chart/
