OK I thought I would do a DIY here specific to E320 CDI as some parts are different from other models. This shows both complete replacement and just replacement of voltage regulator, which in my case solved the issue.

I kept getting "Battery low convenience functions disabled" message intermittently. Took it to Checker O'Reilly and they diagnosed it as being alternator related and not battery.

I purchased a remanufactured 200A alternator from Rockauto and replaced it. It was pretty inexpensive at about $215 (including core charge). But it did not work.

Here is how to remove the alternator. I did not manage to capture all the pictures unfortunately as I did it rather quickly.

1. Disconnect the battery at both the front auxiliary battery and the main battery in the trunk. No DIY for this .. if you can't do these two steps without DIY, stop here.

Remove all the bolts in the picture below with red arrows. Note that the one right in the very center is shorter than the others:



2. After removing the bolts, the front center section can be lifted up.

3. Disconnect the fan connector. There is a big black plug on the driver's side of the car (in the US).



4.Remove clips holding the radiator in place. The picture below shows where the clip would be on the right side of the car. The radiator can slide out from the top but you you will need to move the hoses that are clipped in at the bottom of the radiator and wiggle side to side to get the radiator out.



5.Disconnect intake ducts and water hoses as shown below. There are hose clamps holding the hoses onto the engine side and also the intake from the air cleaner to turbo inlet There is also an electrical connector going to this pipe that needs to be disconnected. The duct on the far left just pulls out. :



6.Remove the serpentine belt. I replaced with a Gates Serpentine belt afterwards (Gates K060888) ~$20 on Ebay. Take a picture of the routing of the belt, it’ll make putting it back together easier. I didn’t take a picture of this part unfortunately. There is a 17mm 12 point on the tensioner that needs to be rotated anti clockwise.

7.Check all the pulleys for play and replace any that are wobbling or noisy while your there.

8.Remove the alternator bolts. There are 5 bolts than are E-torx 12 or a 10mm socket can be used. (Recommend using the proper E-torx bit). I did not take a pic of the alternator bolts unfortunately. I recommend removing the bottom ones first as they will come out more easily. If you loosen the tops first, the bottom ones bind and you need to ratchet them all the way out which is awkward. Rotate the alternator so you can see the connectors, there is a 13mm nut that holds the positive and a 2 pin plug that just unplugs.

Pulling the alternator out is awkward as space it limited. I had alternators in and out of this car 3 times now and this is the best way I could get the alternator to come out and slide back in.



9.I ended up replacing just the voltage regulator.
Below is a DIY for E55 one which is very similar. I wanted to pull the alternator out completely so I could check all the pulleys as well and it is easier to work on the alternator.
https://mbworld.org/forums/w211-amg/...lternator.html

Here is how to replace the voltage regulator on the E320 CDI:

a.Remove the 2 nuts and screw in the pic below (*edit I have no idea why the arrows ended up pointing in the wrong place ... It is the 2 nuts at 3 o'clock and 9 o'clock positions and the screw at the 6 o'clock position):


b.Remove the 3 Philips screws below that hold the voltage regulator in position:


c.Below are pictures of the Voltage regulators side by side. You can see on the old part that the electrodes are worn and much shorter The part number is F-00M-145-292 or F-00M-145-374 ~$86 on Ebay.


10.When putting a new alternator in, connect up the power line and connector to the alternator then use the Star to make sure you can communicate with the alternator. This is an extra step but one I wished I had done since the Rockauto one, I could not even communicate with wit the Star.

11.Install is the reverse of removal. Just remember to plug all the electrical connectors back in.

As I had said, the alternator from Rockauto was faulty and my radiator fan came on high even though the car was cold. I thought it was weird but thought nothing of it. Then I drove and got this message:



I kept checking the coolant level, but it turned out, the cooling fan had burned out. I have another DIY coming on how to fix the fan. A new fan from Mercedes costs anywhere from $690 to $800+ for OEM part number A2115001893. I fixed mine for $125 using OEM part from another car. I will provide more details in a separate thread here: https://mbworld.org/forums/diesel-fo...ml#post6816837