I have a 2010 E550 that started making a marbles sound in the front. I thought maybe it was a pulley, but the noise seems to be coming from the alternator itself. Still, I took off the belt (no noise when ran the engine like this for a few seconds), and the pulleys turned smoothly. When I turned the alternator by hand I was able to hear a bit of the marbles/grinding noise. There's this video online showing how to change it (and that might be enough for me to be able to do it) but I was hoping someone had something a bit more step-by-step. And while I'm at it, are there directions for replacing the ambient temperature sensor? Mine slowly climbs to improbable levels. I'm guessing once I have the bottom cover off I'll see how to remove it, but figured I'd kill two birds with one stone.

Thanks!

 

If you're a confirmed diy guy, the Mercedes work instruction ( manual) and parts catalog is a great resource. Workshop manual, wiring diagrams, etc.

I bought mine off eBay about 4 yrs ago, less than 20 bucks. It came in 4 CD's and is a huge file but it's very helpful in addition to any online videos, etc. I keep it all on a laptop in the garage, handy when working on stuff.

You can search for Mercedes WIS/EPC on eBay.

 

OEM alternator part # 0131545602, outside temperature sensor (OTS b14) 0075421318. See attachments.

 

A few weeks ago I was taking the on-ramp to the Tappen Zee bridge in New York and hit a monster pothole. As I accelerated onto the highway I felt a pretty bad vibration, though it did get a little better as I rode over the bridge. The rest of my drive home though I felt a pretty good shake between 50 and 80. I assumed I bent another wheel. The next day when I started the car though I heard what sounded like marbles up front. I thought maybe it was a bad bearing in a pulley, but when I was reinstalling the serpentine belt I gave the alternator a spin and heard some rubbing coming from it.

So I ordered a replacement alternator from Advance Auto. Oddly, they had a new Bosch unit (shipped directly from Bosch) for $288 after discounts. That’s less than a remanufactured Bosch is, plus it had no core charge, 2 years of road side assistance, and a lifetime warranty!


The OE part is made in GB.


But it's new!

After watching the video on how to replace it I figured it would be an easy job. But once I started working on the car I remembered that the V8 engines are crammed into the engine bay, making the replacement a little more involved. Here’s how to replace the starter on a 2010 E550 4Matic.

To start, remove the HVAC air duct and disconnect the battery. Next, remove the front engine cover, the 2 air ducts, and the cold air intake (this just snaps in place with a couple of clips).







The front grill has to come off, there are 4 clips on the bottom and a single bolt on top. Push them and then the bottom of the grill will swing forward, rotating on 2 hinges on either side. You can then lift the grill up and out of the car.






With the grill out of the way you now have access to the 2 bolts on the front of the car, and 7 on top (you might have fewer if you don’t have Distronic). With those removed you can remove the middle piece of the front-end bracing.






Now you can detach the plastic liner that connects to the fan unit. Just pry it out with a screwdriver.



The liner doesn't actually come out though, just flip it forward.



It will rest here like this.



You can also remove the water hose holder that connects to the heat exchanger.



From the bottom of the car, remove the middle cover and the front cover. The front cover snaps into the bumper, so it might need a little tug to come out after removing all of the bolts. With those out of the way, you can push out the clips holding the fan unit cover. There’s a screw on the right that needs to come out, and you can reach up and unclip the wiring harness (on the left) for the fan unit. This might be the easiest wiring harness to unclip on the car! Check to make sure there’s no hoses zip-tied to the fan unit near the wiring harness.



The instructions show that the fan unit can now come straight up, but on the V8 I had no luck. I had to put a container under the car and pull the top hose out of the radiator (lift the metal clip and the hose slides right out). About 6 cups of coolant came out. With this hose out of the way you can unclip the left and right sides of fan unit and pull it straight up out of the car. I tried to be quick so I could put the hose back in the radiator and minimize the amount of coolant I lost.






With the fan out now you have a millimeter more space to work. You can use a socket on the belt tensioner and remove the belt from the top pulley and the alternator. Now you’re ready to replace the alternator!



There is a wiring harness connected to the alternator by a friction clip, you can just pull it off of the top of the alternator housing.



There’s also a small bolt holding on a bracket that this harness is connected to. I removed this to give me a little more room. From the top you can remove 2 of the bolts holding the alternator in place.






Back under the car you can remove a nut holding a hose in place, and then you can remove the other 2 bolts from the alternator. I wasn’t actually able to remove the bottom rear bolt completely, so I made a mental note to install them (and the bracket) before setting the alternator in place.









Now you can rotate the alternator so that the wiring harness is facing up. There is a plastic cover over the main wire that pops off with a screwdriver, and then you can use a socket to remove the nut and the cable. To remove the wiring harness from the regulator you push on the back and the front should lift, allowing you to slide it off.



Now you can try to play reverse Tetris and try to get the alternator out of the car, pulling it up between the engine and the radiator. I was able to get it by moving it about 6 inches from the left, and then going all the way to the left.






With the old alternator out, now it’s time to warm up your vocal cords so you can begin shouting obscenities at the idiotic engineers that designed our cars who you hope spend a day in hell having to replace alternators in every W212 that ever had one fail.

If you thought getting the alternator out was hard, now you can try to get the new one in, wondering how in the world you ever got it out in the first place. You might think, did this grow? Did I get the right part? It’ll eventually fit into place. Put it in the same position as the last one (there’s a lot of room to move it around once you get it close to where it goes). Connect the positive cable, snap the plastic cap in place, and connect the smaller connector, pushing until you hear it click.






You’ll also want to make sure the bottom bolts (and the holder) are partially in the alternator. I’d recommend you have 2 people for this next part, I had no luck trying to bolt the alternator in place by myself. How I finally got it was to have one person under the car holding the alternator in place, and one on top trying to line up the bolts and getting them to actually mate with the hole. While you’re doing this, make sure the bottom bolts don’t fall out of place (I used painter’s tape to secure them).

After tightening all 4 bolts I’d go back and make sure they are all secure a second time. To install everything else, just follow the instructions backwards. I put about 400 miles on my alternator after making the initial grinding noise, with the unit having a total of 177,000 miles. The brushes on the voltage regulator still have a bit of life in them, the front brush is about .25 inches, and the back a hair under .5.

 

 

Odd thing was, the sensor (while defective), was also installed upside down! I have no idea how that could have happened.