ML 350 wont start…guess what. It’s most likely the voltage regulator. Read this before you buy the whole alternator

Don’t you just hate getting stranded in the middle of nowhere? I mean even if you know exactly where you are it’s really annoying We’ll this just happened to me. I took my family out for a quick walk at a local flee market and “click” tried it again and “click” again. I mean, damn, I thought for sure I wasn’t going to hear that on a Mercedes-Benz. We’ll I was wrong. No knock at my ML, it’s actually been a very good vehicle to us. Except for this issue with what seemed to be the alternator, it’s been really reliable. Once, shortly after we bought it the crank shaft sensor went out and it would crank and crank and not turn on but fortunately it was still covered. Got it fixed and didnt have any issues till now with the alternator.

Here’s some background on what you’re going to see on this post. I actually started it a while back. We’ll more than a while it’s actually been a couple years. I had this issue with my alternator back in 2010. What I described above, did in fact happen about two years ago. I managed to have road side assistance give me a boost and I got the car running again just long enough to make it home and just as I expected it didnt turn on again. At that time I was in a hurry and it got me by surprise. What I ended up doing after pages and pages of reading on the internet about what the problem could be was looking for a voltage regulator. Everywhere I read, it seemed that the alternator would be fine and the problem was the voltage regulator so I set out to find one. Luckily, I found one over at Auto Parts Warehouse. Everything was perfect except that I didnt have the time to wait for the part to come in. At the time it was my only car and I couldn’t be without a car for days so I opted to find a voltage regulator locally.

Good luck finding a shop that carries it. I tried all of them and they all said they had to order it. We’ll I can do that and for less than what those guys wanted to charge me for one. I ended up calling rebuilding shops and they said no. I had to take the alternator in and they would bill be to rebuild it and put one in. Which is what I ended up doing.

Forward two years and the junkie voltage regulator they put in dies again. Which gets me to where I am now. With different symptoms but the same problem.

Here’s the symptoms my ML 350 had when the voltage regulator went out the first time. NONE! Yes, you read that correctly, none that I noticed. The morning we left for the flee market everything was fine and when it was time to leave the dreaded “click” happened.

The second time around there where symptoms. Here’s what started to happen:

  1. Obviously the battery indicator would turn on and go off.
  2. The system seemed to skip a beat. Once in a while the electrical seemed to miss a beat and the whole car would like shiver a little. The battery indicator would light up while it shivered and turn off. (Note when this happened, I went online and ordered the part) You really can beat the price about $50 bucks to fix your car is not a bad deal.
  3. The last and might I add the worst one. I literally got home and didnt drive the ML again till I fixed it was when I was on the freeway and all my dials just dropped for a moment and then everything came back on. That was weird! Then it did it again in about a 2 minute time frame. Luckily I was able to get back home and I started working on it the next morning. By then the part had arrived. Which really surprised me. I expected the part to take longer to arrive but it arrived in two days from the day I ordered it.

Thankfully the symptoms saved me a battery the second time around. To what I understand the first time my voltage regulator went out it over loaded the system, including the battery and made it poop in a sense. It actually had a crack down the side and I had to replace it along with the alternator. All in all I spent about $250 on the whole thing. I changed the battery and took out the alternator and took it in to the rebuilding shop to have them, supposedly rebuild it.

Now, two years later, you might ask how do I know it was a junkie voltage regulator. We’ll it lasted only about two years for starters. The first one that gave out happened a good 6 years after I bought the ML 350. Oh and when I took it out it looked really cheap. You’ll see in the picture below what I mean.

Here’s the steps I took to replace the voltage regulator on my 2004 ML 350.

Disconnect the battery, loosen and remove the red wire from the battery.

remove the passenger side front tire.

Now remove the black liner wall, there’s 6 plastic nuts that you’ll have to remove.  Once removed you have to wiggle the liner off.  It’s easier if you start removing the part of the liner thats closest to the front of the car.  Then work on the section closest to the door.


here’s a shot of one of the sections you’ll have to remove a plastic nut.

nuts off.


Liner off, now you’ll have direct access to the alternator.


There’s the alternator you’re looking for.  Before you get to remove it you’ll have to remove the belt you see there on the right side.  There’s a tensioner that keeps it nice and tight.  The picture below shows you where you’ll find it.


Here you see the pulley that’s the tensioner.  The nut in the circle is where you’ll put your socket wrench and turn counter clockwise.  The nut wont actually turn because it’s not a nut it’ll just move the whole pulley to the left which will allow you to slide the belt off the tensioner.  Look below.


Here you see the belt already off the tensioner.  Now you can go back to the alternator and slide the belt off the pulley on the alternator.


Once the belt is off the alternator pulley you can start removing the electrical connections to the alternator.  WARNING again remember to remove the battery connectors before messing with those connections.  I’m sure you understand WE ARE NOT RESPONSIBLE FOR BONE HEAD MISTAKES.  You take full responsibility for fucking around with your car…..alright now that that’s done with.  Lets move on.


Remove the black cap on one of the nuts and put it somewhere safe.  You’ll be putting it back after replacing the voltage regulator.


Now, loosen and remove the two nuts marked on the picture and disconnect the electronic connector on the bottom left of the alternator.  That’s all you’ll have to worry about here.  Now you’ll move on to remove the screws that hold it in place.


Here’s the image with the nuts off.


The top screw is not problem, it’s easy to access and remove.  Just be careful to not sure a tool that’s to long and damage your radiator   Keep in mind those are not regular bolt heads.  They’re the star type.  You will need a set of Torx sockets.  The bottom one is a bit more fun to remove.  Lets keep going.


It’s tough to photograph this sucker while it’s screwed in but this should give you a good idea of where to find it.  Unscrew it all the way and slide it all the way out. You’ll notice that there’s a sort of fitting that the screw goes through to fasten back in.  Keep those two in mind, we’ll talk about those again, soon.

For now you’re going to have to carefully wiggle the alternator out of the space it’s in.  It shouldn’t just fall out when you take the bolts out.  In my case it took a bit of working it to get it out.  Damn, all this trouble for a little $50 buck voltage regulator.

Let’s get to work on that bad boy.

Once it’s off here’s what you’ll have.  Pretty scary huh.  Not really it’s actually a lot simpler than you think.  Here’s what you’ll do.


Remove the two nuts and the screw that keeps that plastic protector plate.  Make sure to use the correct size tools.  You don’t want to mess up those three pieces.


Once it’s off it’s easy to see what you have to do to remove the voltage regulator. By the way, it you don’t know what it looks like, don’t feel bad I didnt either.  It’s the black plastic piece that has the electronic connector.  All you have to do at this point is just remove the three screws.  Just keep in mind where you pull them from.  One of them is shorter.  The lighter one on the left of the picture is the smallest of the three.  I’m my case it was a pain in the ass to remove one of the other two.  Remember when I mentioned that I took it to a place where they put a piece of crap voltage regulator, you’ll notice that that voltage regular that’s on there doesn’t even have a manufacturer or part number…nothing.  Pretty clear indicator of a trashy low quality part.  Also, you’ll notice that the top screw is already stripped before I even touch it.  Thanks again to that shop I took it too.  Removing it was a nightmare and I ended up just replacing the bolts with new hex bolts as you’ll see below.  Once you have those three out, you’ll just slide that voltage regulator out and chuck it.  Slide the new one in and reverse the steps.

Here’s the alternator with the voltage regulator removed.


Here’s  a shot of the new voltage regulator in place.  Notice the brand spanking new hex screws and you’ll also notice that this voltage regulator actually has branding and markings.  Also, the picture doesn’t show it but remember to put all three of the screws that you removed.  My truck ran for a good 6 years and about 50,000 miles before it had any problem with the voltage regulator.  I expect the same this time around.

And here’s the last shot before it was on it’s way back into the truck.  Plastic plate back in place and everything fastened nice and tight….but don’t get to crazy on the plastic pieces.

Now, just reverse all the steps above and put it back together.  That’ll take care of the problem.  When you go to put it back in the truck you’ll notice that you’ll have to press out the two pieces that help align the bolts that hold the alternator in place.  In that it’s easier to press them in with a C clamp slowly than trying to bang them in.  You’ll see what I mean whey you try to put the alternator back on.

The main thing is to have your voltage regulator ordered quickly once you notice the symptoms.  They’re inexpensive and easy to replace, you just have to make the time.  You can find it by clicking on the image below.

ml voltage regulator

Click image to find your voltage regulator.


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