I'm not a mechanic but i've been attempting to fix my Mercedes Benz 2003 W211 E320 with a few changes to minor parts, one of which seems to be the alternator as it's no longer charging the battery properly.

This is my car:



My first attempt was changing the Voltage Regulator on my current alternator, which at first seemed to work fine, after the new Voltage Regulator was put in my headlights stopped flickering
and there were no warning indicators that it was not working as it should.

This is the Voltage Regulator that i bought and put in on my OEM alternator (i assume it's OEM at least):
https://www.ebay.com/itm/152003628392

However when i went for a test drive the first 30 minutes were fine but as i reached the 45 minute mark i began to get warnings about the battery on my dashboard, so i went back home and noticed that the battery was not being charged.
To me this made no sense as the Check Engine light had gone away after the new Voltage Regulator was put in and it did not come back on again even after the check battery warnings started showing.

After this the battery stopped charging and completely dropped all the way down to 5v after sitting for a week, which in turn made me look to replace the alternator,
however no matter how much searching i do around the internet i cannot find the correct alternator to use for my vehicle.

So out of desperation i am now posting here in hopes someone can point me to the correct part to use.

According to a question i asked on Amazon for this part:
This is the response i received:
AL0789N is compatible with AWD 2003 E320 sedans. If you have a RWD version, Bosch AL0788X is the compatible alternator.

Unfortunately i may have ordered the wrong part as i purchased this alternator online recently which does indicate that the Manufacturer Part Number is AL0789N, did i buy the wrong part?
https://www.ebay.com/itm/351928273854

And is this the correct part?
https://www.ebay.com/itm/175978028154

As i live in the mountains having a car that doesn't function properly is a big issue, so i have spent the past week trying to do proper research and fix this issue but i guess i simply don't know enough. Please help

 

After some more research i have noted that the voltage regulator that i mentioned above (the one i used as a replacement) seems to be specific to Eng. Code 112.949, which in turn is the
exact engine number recommended for the AL0789N alternator.

Which most likely indicates that the voltage regulator i used, was not the correct part for the alternator i currently have.
This leads me to believe i actually do have and need an AL0788X alternator, which seams to be indicating it uses Eng. Code 112.941

 

Very interested in the outcome. I may need to check the alternator on my E320 soon.
I assume you checked for the OEM number: https://mb-teilekatalog.info/
Did you test the alternator voltage output at the alternator?

AL0788X is rated 120 Amps
AL0789N is rated 150 Amps

My E320 (4-matic, 2004 EU) - 211.282 is supposed to have a 150 Amp alternator:
alternator: A0121541302
regulator: A0031545406
No idea if other build version have other alternators.

Is voltage dropping in the battery related to the alternator? I thought it was just related to the battery itself - or potentially some electrical leak?

I would have some ideas on how to figure this one out, but I probably better wait for some experts to answer

 

Unfortunately i can't seem to find my exact model using this website : https://mb-teilekatalog.info/
I may just not know how to navigate the site correctly to find my model but i've looked under E class (i.e E320) and there are no engine numbers matching 112, they are all mostly 200's

The battery should technically be being charged while the car is being driven, so the fact that the battery was dying while i was driving most likely indicates the voltage regulator was not working properly in combination with the alternator i have.

My guess is in combination of the AL0788X alternator and the AL0789N voltage regulator, i.e voltage below

AL0788X is rated 120 Amps
AL0789N is rated 150 Amps

The voltage regulator expected 150 Amps but since the AL0788X alternator only gives 120 Amps, the voltage regulator wasn't working correctly.

 

Find your car here: https://mb-teilekatalog.info/?lang=E...arkt=AG&mmod=E
Alternator can be found under electrical equipment.

Enginge: https://mb-teilekatalog.info/index.p...arkt=AG&mmod=M

This would be the transmission:https://mb-teilekatalog.info/view_Gr...mno=0&group=27

Did you check the voltage on the BC?

I would still first check the output voltage at the alternator. Before taking it out. It might be something else.

 

What's the vin? Normally you punch it into EPC and get the MB part number for your alternator and then cross reference that to whatever the Bosch part number would be. You can get a knock off copy of EPC/WIS on eBay. It kinda stopped in 2018/2020 but should still work for a 2003. Also the other issue with older pre-face lift cars is that the battery control module can also go. Not there in the post face lifted cars.

 

Yea i checked the site you linked and there's no E320 model listed that has 112 as the engine number, they are mostly all 200's

 

If i look under motor, this would be the correct alternator info based on the engine number (i.e 112.941):
https://mb-teilekatalog.info/view_Su...=15&subgrp=030

Unfortunately on my car model it will not display the voltage on the dashboard but i have used a multimeter and it does read 14v when the car is on, for the trunk battery.
This is with the original voltage regulator in place (which i could clearly see the pins were very worn down when i removed it when attempting the voltage regulator replacement)

 

I did try to use a VIN decoder but it didn't really give me much information, it could have been the site i used
Can you link the best site to use for VIN decoding for the information you mentioned?

 

Just post the vin. You can get a copy of the Mercedes EPC/WIS on eBay, as low as $7. It's several gigs and takes a while to download/setup. You don't get it from a vin decoder. EPC is the electronics parts catalog. You put in the vin and then drill down to the part you want and it tells you the right part number for your car. It's why if you go to the parts counter at the dealership, they just want the last few digits of your vin so they can just look it up in the parts catalog. They usually don't tell you the part number though, they don't want you to use that to buy it cheaper online.

 

Update #2:

Initial indicators something was wrong:

• Electronic Consumer notifications (i.e turned on / turned off) occurred regularly, generally every time i drove the car
• Electronic Consumer would turn on at car start and then back off a short while after driving the car, sometimes it would last a while and other times it would turn off right away
• Internal / External lights would flicker while the car was running
• Check engine light came on at the same time the light flickering and Electrical Consumer notifications began appearing

Stage #1:

• Old battery was holding at 11v prior to draining down to 5v after attempting the alternator replacement
• Took old battery out of car for charging
• Charged old battery to full (i.e 12.8v) with car battery charger (i.e Schumacher)
• Put old battery back into car (i.e disconnected aux battery first, reconnected trunk battery, then reconnected aux battery)
• Started car, no internal or external flickering for the lights, no check engine light, no warning notifications, etc.
• Tested voltage on old trunk battery while car was on, returned a little over 14v
• Drove the car for 40 minutes, no issues or notifications on the dashboard

Stage #2:

• Replaced the old trunk battery with a new one (i.e interstate > legend, both AGM)
• Started car, no check engine light, no battery warnings, etc.
• No Electronic Consumer notifications while car is running (i.e turned on / turned off)
• Turned on the air for like 10 minutes, check engine light came back on
• No noticeable flickering on the internal or external lights with new battery
• Drove the car for 40 minutes, no issues or notifications on the dashboard

What i have not checked:

• I did not check the voltage on the trunk battery, while the car was running, after the check engine light came back on

Conclusion:

• Considering how worn the pins are on the original voltage regulator, it simply may not be properly charging the battery over long periods of use
• While replacing the battery solves the immediate issue of being able to drive the car, it does not solve the long term issue of the voltage regulator most likely not properly charging the battery
• While the old and new battery show no immediate issues over the 40 minute drive, the alternator may not be charging the battery or properly charging the battery
• The old battery most likely was going bad due to improper charging or battery age, which is why it drained so quickly when disconnected from the car
• When using the internal air system, there's most likely more voltage being pulled from the battery / voltage regulator, which is why the check engine light came back on
• With the original voltage regulator in place and the check engine light back on, it's definitely telling me there's something wrong with the voltage regulator (at worst, the alternator)
• With the replacement voltage regulator (the incorrect one) in place, there was no check engine light on, during the test drive mentioned in the original post and after when the battery warnings started showing

At best, i only need to replace the voltage regulator, at worst i need to replace the alternator itself, however even if i want to change the just the voltage regulator, i need to know what alternator it needs to be for.
As i do know the alternator is BOSCH and the voltage regulator is also BOSCH (i.e as indicated by the branding on the part(s) ), i'd have to guess it's the one i indicated in the original post above.

With the Eng. Code 112.941 showing an alternator that uses 120amp and verifying that on the catalog you linked
i.e https://mb-teilekatalog.info/view_Su...=15&subgrp=030

I'd have to guess that is in fact the correct amps at the very least.
I'll most likely have to pull out the current alternator and look for any part numbers on the actual alternator / voltage regulator to probably find the correct one to use, because looking online is not returning accurate results.

 

The first link only links to the car - here you will find the alternator.
The second link goes to engines. (since many models used the M112 engine)
Same goes for the 722.6 transmission (third link)
If you enter your VIN at the top of the homepage, you will get your model, engine number and transmission number and type.

 

Ah ok thanks for that info!
I didn't even see the VIN search at the top lol i must be blind Thanks for pointing that out!

Using the vin search i get back:

Sales designation: E 320 [MODEL_IDX = 0]
Market: NA,North America
Engine no.: 112949 31 524600
Transmission: 722618 04 309795 [transmissionType = GA]

SA code
040U - BLACK
M112 - V6-GASOLINE ENGINE M112

So it seems since my engine number is 112.949 then i did in fact buy the correct alternator and voltage regulator
So why was did the old battery die during the test drive? I have to assume the battery voltage dropped too low when i was putting in the new voltage regulator (i.e down to 10v)
Even though you'd assume the battery would charge during the test drive if it was the correct voltage regulator? I guess i would have to test it again but now with the new battery i bought.
This could in fact just be a case of the battery going bad in combination with the voltage regulator needing changing.

The only downside to the catalog is that it doesn't show much info on the alternator for engine number 112.949
https://mb-teilekatalog.info/view_Su...=15&subgrp=030

 

As mentioned: the alternator details are in the "car" link, not in the "engine" link.

follow this link and select your car. Should be 211 + the next 3 digits of your VIN.
Alternator under "ELECTRICAL EQUIPMENT & INSTRUMENTS"

If you have trouble finding it, feel free to send your VIN (or at least the 1st 6 digits) on private message.

 

I think you mean the last 6 digits of the vin. First 6 doesn't really tell you anything.

And yeah, not sure why there's all this head scratching going on, easy way to see is EPC with your vin number, takes a minute or two and you're done. Could also be the battery control module.

And if OP doesn't want to share the vin with anyone, the new system is ISPPI, but a $7 knock off of the old EPC on eBay is cheaper. I think ISPPI is now $79 for one year.

https://www.startekinfo.com/help/faq

 

I believe this is it then, i used the identification number which shows after searching the vin (i.e Identification number: WDB211065...),
i also noticed there's a small button with the 211.065 info which leads directly to this link (i.e right under vin search results header text):

https://mb-teilekatalog.info/view_Su...=54&subgrp=026

 

Do you happen to know what the battery control module would be listed under? I assume electrical equipment?
https://mb-teilekatalog.info/view_Gr...11065&group=54

 

No idea, I'd just use EPC. You're just making things harder for yourself. I could tell you in 2 minutes if you'd like to know the part number. All I need is the vin number, you can pm me. Those catalogs are just a guess, the MB database in EPC would be the most accurate. Or get a copy of EPC yourself on eBay.

 

It was under control modules and relays in trunk. Looks similar to EPC. But EPC would be more accurate because you're using the actual vin number and not a range so you'd get the exact part number. But while there's 3 different part numbers for the voltage regulator depending on what alternator you have, I think all the battery control modules are the same, they just kept revising it so there's a bunch of different part numbers.

Try this thread

https://mbworld.org/forums/e-class-w...ery-drain.html

Tried one 2003 car for sale and used that vin number seems like they all used the same battery control module and it's no longer in stock but you can get them on eBay in the $100 range.

 

Update #3:

Step #1

• Car sat idle / unused for 1.5 days
• Checked the voltage on the trunk battery, returned 12.6v
• Turned on car, checked trunk battery, returned 14v
• Took out alternator, changed the voltage regulator from the original part to the part i purchased (i.e indicated in original post)
• Put alternator back in, turned on car and tested light output (i.e no flickering)
• No notifications or warnings on the dash
• Checked trunk battery voltage, returned 14.1+ volts
• Test drove the car for 1 hour, no issues or battery warnings (i.e like the first drive test)
• Tested using the internal air for 10 minutes while driving, no issues
• Tested trunk battery voltage again upon returning from test drive, returned 12.8v when car was off, 14.1+ volts when car was on

I will note that the Check Engine light seems to do this pattern where it will turn off IF i disconnect the trunk battery at any point and then will eventually turn back on again, after a bit of driving or starting the car repeatedly.
Since i don't see any obvious issues with the Alternator itself, i have to assume the Check Engine light pertains to something else.
However the Alternator did look pretty dirty / old, even though it is in fact returning the correct voltage.

I took these pics while taking off the Alternator cover.







So with that i can confirm the Alternator is 150amps and the Alternator i purchased (i.e linked in original post) is definitely the correct one

Taking out / putting back in the Alternator only took about 1.5 hours, so not too bad and with the right tools it was rather painless to do.
This was doing so from the top / inside of the vehicle and not from underneath, which is what i attempted to do the first time for just the voltage regulator, which was a pain in the ***.

So don't be a fool, get the right tools!

 

how did it go I got 2004 e320 4matic and bought regulator youtube said on my model and some models i can put it in without taking alternator out i cant see how do you know ?

 

You can technically go in from the bottom of the car (i.e remove bottom shielding) and the Alternator is accessible that way, however you'll need very specific tools to un-do the Alternator cover (i.e different bolt sizes, Philips screw, etc.),
take off the Voltage Regulator screws and put it all back together again.

Considering going in from the bottom, there is a lot less working space than going in from the top / inside. I highly suggest you buy the right tools and take the Alternator out, it's not as much of a hassle at it first seems
You can of course take a look at some tutorials if need be (i.e youtube, etc.)

Although your models engine layout may different from the 2003 version, so a few things to consider but if the layout isn't much different, then i'd do the above ^

Tutorial (bottom): Tutorial (top):