Was in dyno mode for other reasons and when i scrolled to the voltage screen i noticed my battery voltage was randomly fluctuating from 12.5 to 14.5 about every 5 seconds. Car seems to drive normal and starts up fine.

When this happened on my SL55 / M113K vehicle it was a bad voltage regulator which was replaceable by accessing the alternator from underneath the car.

Anyone here have a W212 E63 (2014-2016) that you replaced the voltage regulator and/or alternator and have a DIY link to the job? Searched the forums and youtube and seems nobody has run into this which is surprising.

 

It's funny you bring this up as I literally just did mine "just because" while I was experimenting with the GinDistiller method of doing motor mounts. This can be done on jackstands with relative ease provided you have the skill and tools to drop the power steering rack.

To get to the regulator, you need to drop the powersteering rack.

First step, after you lift the car secure the steering wheel with your seatbelt BEFORE you drop the power steering rack. If you don't, the steering wheel will need to be physically reset/realigned for steering rack reinstall. Doing this will make your life easier.

Next, follow GinDistiller's writeup to dropping the power steering, including removing the driver's side downpipe. You don't need to drop the passenger side.

https://mbworld.org/forums/w212-amg/...nt-review.html

At this point, you're staring at the back of the alternator.

Remove the power cable and plug from the alternator. Once this is done, it's time to remove the cover.

CAUTION!! A replacement cover is not available. You'll need to CAREFULLY pry it off. In doing do, you will break a few tabs off of the teeth that hold it on. It's unavoidable, but can be generally managed.

Once this is done, the voltage regulator is exposed. Remove the 3 bolts holding it in and it’s out.

On the new regulator, you'll notice thr round part with an opening popped partially up like a tab that can be pressed. DON'T PRESS THAT DOWN UNTIL YOU BOLT THE REGULATOR IN. It holds in the contact to the regulator, and the regulator can't be installed with this exposed. If you do muck up and press this part down before install , it can be reset using patience and small picks/ flat head jewlers screwdrivers.

Install the new regulator, press the tab down til it clicks, reinstall everything from this point on in reverse order, and you're done.

Cheers.

 

@jvakos what were the symptoms of the bad regulator on your SL55?

 

@WANTED!! hey man thanks and super helpful write up here. Bummer this isnt as easy of a job as it is on the M113k where you can get the VR from under the car and swap it out in about 20 mins, or just remove it outright from the top of the car in about an hour or so.

Were you seeing your voltage readings to fluctuate a lot (12.5 - 14.5) and replacing the VR solved that? I am assuming it should as if it was the alternator then the battery wouldnt be charging properly and the voltage would be more steady but declining 12-13 range since its not charging properly.

I've never touched the power steering rack but will look into those instructions you forwarded from gindistiller! Thanks again!

 

@PeterUbers you often can tell if you have a bad voltage regulator if the voltage reading is fluctuating a lot while driving (11.5 to 14.5) and your lights and or AC fan can flicker too. If its the alternator then your voltage will just steadily decline which was actually my case in the SL55... was at 13.5 then wouldnt charge above 13 then 12.5 and had to continually trickle charge the battery to keep it between 12-12.5 since the alternator was bad and not charging even after a new VR.

 

Never checked. However, I recently having sporadic electrical issues associated with fluctuating voltage that made me suspect it was probably about time. Since I was going to be down there anyway I opted to just do it. Turns out my old one was right on the edge of bad contact that my gut instinct was proved right.

And yes, the w211 e55 was stupid easy by comparison.

 

Could poor voltage ever contribute to misfires?

 

It could, but not always. You'd more likely get p0300 (multiple cylinder misfires detected) over individual cylinders. Typically you'll start seeing sporadic electronic twitchiness, sometimes random codes pop and then clear. As stated by jvankos, if you watch your voltage in developer mode you'll be able to observe voltage dropping and rising by a fair amount. If you're getting just misfires, really rule out everything else prior to assuming the voltage regulator is to blame.

Unfortunately, a failing voltage regulator and a failing alternator show similar symptoms. Usually its the regulator, but not always.