thanks @Tommyboy928 - is the K57 relay the one in the trunk by the battery or the one/fuse in the passenger footwell? my car is 75k miles and i'm 3rd owner and its been garaged in Chicago where i live so dont think the battery terminals have been corroded but good call to check those. my starter batter is definitely old think its a 2017 and my start ups are noticeably slow so may try to replace that and see what happens.

i.m going to take it back to advance auto where i bought the rear battery and have them test it along with testing the starter and alternator which they said they'll do for free. i do have a decent amount of accessory belt squeal at start up but it goes away after about 10 mins as i think that belt has residue from the pentosin that leaked just before i had the ABC ripped out and replaced with Silvers Neomax coil overs. there is always something going on with these R230's thought i solved for most of it after dumping $3.5k to do the coil over conversion and now the electrical / battery problems rear their ugly head. ugh

 

10 min sound from belt is wrong, then its bad tensioner ,or belt is to long. this need be fixed. Tensioners with new pulley is cheap on aftermarked .
k57 is in trunk up rear right side, passenger side .

https://www.benzworld.org/threads/au...lease.2726041/

 

@Tommyboy928 thank you for that insight and I checked the serpentine belt and as you suggested it’s definitely a problem…. I’ve got oil leaking on the belt it’s slightly dripping from the oil filter housing directly onto the serpentine belt tensioner pulley. Am assuming the belt is slick and not turning the alternator appropriately to charge as a contributing factor so have ordered a new belt to rule that out……. Next will be the K 57 and checking the VCM which I’m not looking forward to doing. Will update you shortly. Thanks again I really appreciate the help.



Oil leaking on serpentine belt, tensioner pulley


here’s a photo. Just orde

 

Check that whoever fitted the last oil filter fitted and seated the o-ring in the filter housing correctly. It's possible they crunched the o-ring - it needs to be eased into place with plenty of clean oil to bed right.

Slow cranking probably weak front battery or, less likely, starter. Jump start it with a known good battery and listen for cranking speed. The battery can be on its last legs and still turn the starter pretty well.

 

quick update - i did have an oil filter housing leak which was the cause of the oil drops hitting my accessory belt. thanks to some DIY's on these forums I changed all 3 oil filter housing gaskets and cleaned up the oil that dripped and everything is fine on that front and no more leaks on the accessory belt.

i also just bought a new starter battery as apparently mine was bad and i just installed that. car is still only holding around 11.5-12v and very slowly drops to about 11 after about 45 mins of driving so at this point i am assuming its an alternator issue? i replaced the voltage regulator last year when i had some charging issues and that temporarily fixed the situation. i'm at 75k miles and seems this is about the timing for when alternators go out on Benzes.

i am hoping this is only an alternator issue and not BCM... will report back when i get the new Bosch alternator installed and fingers crossed the charging goes back to normal.

 

The rear battery is charged directly from the alternator. That is what you should test initially to check the charging system. It should come up pretty quickly - but not instantly - to about 14 Volts. The slow rise indicates correct battery internal resistance and is telling you that the battery is probably good.

The front battery is a different story: it is charged via a DC-DC converter in the BCM which monitors the front battery condition and charges when needed - so you should, but may not, measure a charging voltage on the front battery. It is safe to say that if you don't measure a charging voltage on the front, after several attempts, then the BCM is probably bad. Certainly mine always shows charge on the front battery after starting.

If it is the alternator then it is probably just the regulator in the alternator, rather than the whole unit that is suspect. You can buy a new Bosch regulator.

So test the charge on the front battery, and the 100 A fuse in the prefuse block which, if blown will prevent charging.

 

Thanks Tom Manning, I am reading/learning too!

 

thanks @Tom Manning super helpful info about the BCM. My handheld Amazon grade battery tester says the front battery and rear are charging but it gives an alternator “low” sign so maybe it is just the voltage regulator. Replaced that a year ago but I’ll try replacing it again since that’s a fairly simple fix from under the car vs attempting the alternator replacement which is doable but much more involved from what I’ve read.

I love this car but it can really test your patience with the frequent ABC and electrical issues!!!

 

quick update - still sorting out my lack of battery charging issue and thought it might be the 100 am fuse in the passenger footwell. Was a bit fussy to get to it (about 45 mins to remove the different covers, sub woofers etc and 45 min to button it back up) but to my disappointment the fuse was perfect and not the culprit that I thought it would be.

So next is the alternator.... with no codes showing my guess its the voltage regulator or alternator.

This damn car is like dating a younger woman - fun as hell, always fussy, expensive and never without drama !!!!!

 

You forgot, "she's liable to stab you while you're not looking ...."🤣

 

Don't know if this will help but I burned up/melted a BCM once on my w211. This was on a 2006 E350 4matic. I bought it with a salvage title as it had been involved in a collision and had sustained front end damage. When I first got it a couple times it just died going down the road. Each time it died I found that the rear battery was bad. I was on my third new battery in about 3 weeks when the BCM toasted. I was able to determine that this was all caused by the wire connecting to the starter shorting out. I found this wire connection was extremely close to a piece of exposed metal. This would short out and take out the battery. When I put in the 3rd new battery (always the rear) it was still shorted and it took out the BCM. I used a pry bar to clearance the connector a bit. I put in a used BCM and the car has been driven over 50,000 miles since with no problem. The car now has over 180,000 miles and has been a great car. I do not know what caused the clearance problem to begin with. Could have been the collision or maybe motor mounts but I never replaced any motor mounts and they have no indication of being bad. The wire that was shorting out was the main wire to the starter and this is not fused. I don't know if this will help anyone but might give you something to think about.

 

It’s a totally different system, the w211 essentially has one battery, the r230 has 2 it uses every time it runs.

 

I have been watching this thread for a while. Lots of good information.
The KEY to troubleshooting the system is to understand how it is suppose to work. If you don't... most of your effort is in vain.
I have a 2003 SL55 AMG that has had the dreaded RED battery light on since I purchased it. I tried ALMOST everything to fix it.... new alternator, batteries, K57 and K75 relay., 100amp fuse under the floor...etc.
In the end.(after questioning the previous owner SEVERAL times).... he had inherited the car and really knew nothing about it. He had put a cheap battery in the trunk that had drained quickly.. so he jumped it many MANY times!!
The BCM was toast! Installed a new one... Problem solved!!!
Of course he told me when I bought the car he was driving it DAILY to work. This was not true!!!
The first rule of buying 20 year old COMPLEX cars..... most people will not be honest!!! Buyer beware!!!!
With all that said... it is a great car that I love driving and maintaining!! I have learned a LOT!!!!
Down load the Dual Battery explanation.. read and understand it. Actually kinda fun!!!!
Best of luck!
Mark

 

And - as has been said many times, but bears repeating - jump start the car from the front battery only.

That's from the manual, so it's good enough for me.

 

Jump the front battery AND...I attributed my BCM issue to NOT disconnecting the trunk battery while jump starting the car (due to a dead/old starter battery). I used two battery maintainers (one on each battery) for 5 years of ownership before the incident and (knock on wood) have continued to use trickle/maintainer since.

 

You shouldn't have to disconnect the rear battery while jump starting, although you can start and run the car without the rear battery connected.

Doubling up batteries doubles the current available to the starter while the voltage stays constant. Most likely your BCM issue was unrelated.

 

I interpolated the warning on page 360 from "just charging the front battery" to include jump starting.

 

There's a bit about jump starting on another page. Usual precautions apply.

I never noticed the warning about disconnecting the rear if you want to charge the front though. I wonder if incorrect charging could be causing the fried BCMs?

 

That's the first time I've ever seen or heard that mentioned as well. Personally I think with this electrical system you can't be too careful. Nobody really knows for certain what is Ok to do with it, just what should be OK.

 

100%

For those worried about the risk for damage via a jump start, a suggestion would be to keep a 10mm ratcheting wrench and one of these in the car:

If ever in a situation where a jump start is actually needed, just disconnect both batteries (in the correct order) and let the boost box quickly bring some energy back to the starter battery.

 

My BCM fried a few months ago: apparently a previous owner had installed a cheap Duralast alternator, don't know if that caused the issue or whether the dealership fools where I'd bought the car had damaged anything by jump starting the car. But they know nothing about Benzos so I wouldn't be surprised if they did jump start the car, or let the battery drain then charge it wrongly. But suddenly as I was driving along, the alternator began putting out 20 Volts (too much) and I got a big red STOP!! BRAKE on the dash. This was the SBC shutting down due to wrong voltage. My first thought was "Oh great, the sensatronic brake unit's gone bad" and Mercedes can warranty replace that. But that was just the first system on the car to detect over-voltage and therefore shut down. New alternator, this time a good Genuine New BOSCH. and a new BCM, I guess those cost around $600? And the car is perfect again. Of course since it is a 2003 SL55 AMG with 92K miles, while replacing the alternator, the shop guys found the dual idler pulley which costs $710 from Mercedes, was badly worn (my indy shop guys found me a new genuine MB part for $300) and also the water pump was about to explode! Its bearings were bad. (I had been hearing bird-chirping from the pulleys for a minute on startup and thought an idler pulley was wearing out...) So it was good that the belts/pulleys were getting attention, otherwise soon the water pump could have just quit and you certainly don't want that to happen! Car is like new again, and has all new coolant and new belts as well. Rule of thumb: Never buy cheap parts for the R230. A Duralast alternator from Autozone is simply stupid. Buy new and genuine Mercedes or Bosch, for alternator, water pump, etc. It's a $130,000 car, and should be treated as such. Maybe for the previous owner it might have been his only car, and the Duralast was the only immediately available part, or an indy shop run by monkeys chose parts for him. Who knows!
I will never jump-start a Mercedes. If there's a problem, I'll remove whichever battery, and either recharge, test or replace with new, and carry on. And never use the car to jump start someone else's car!

 

does this happen with the r231 as well?

i have a 2017 and i bought a charger for use when im away and one or two people said you shouldn't charge the battery using the jump start connections under the hood, even though the manual states to do it this way.

 

Your car has a different system. Follow your owners manual not what internet posters say.

 

thanks they must have corrected the issue then, I assume.

 

Another one on benzworld. Still an isolated incident?