speedracer.eric

The issue I'm having is that the voltage seems to go all over the place when I start driving, or the RPM changes. When the car idles, it seems to be fine for a while @ around 13.5V. Then I start driving around the neighborhood and it drops to 11.7V or so. It doesnt come back up every time I stop, but most times I came to a stop, the voltage went back up to around 13.5V.
I replaced the batteries first, both the trunk (Oreilly Part # 49PRMJ) and the aux (Advanced Auto- Part No. TX14) under the hood.
Kept getting low power, no convenience functions. Took the car to have the alternator and batteries tested, found out the alternator was only putting out 65 amps. Bought a bosch alternator (Part# R111202A) at Oreillys auto parts, puts out 150 amp. I didnt know until just now reading these forums that there are two units that fit (bolt on) and I have no idea what came off the car originally or how to find out.

Writing this post, I also realized that the battery I asked for was supposed to be 900 CCA, but the battery they sold me was the 825.

I did jack up the car and the terminal post on the alternator seems nice and snug, any thoughts or pointers would be greatly appreciated!

kajtek1

I would not worry about slight difference in batteries.
You can subscribe to EPC or go to a dealer and with your VIN you will find precisely what parts belong on your car.
Advanced Auto is not going to work here.

speedracer.eric

Subscribing to EPC doesn't look easy, I must contact a secretary?
Are you saying the aux battery I bought at advanced is not compatible with my vehicle?

kajtek1

How should I know?
You bought it.
But your description indicate charging problem, not holding problem.

AMG WORLD

One thing you need to understand about your Mercedes, it does not like anything else but OEM! So if its not OEM atleast match the cranking power at 900 for the bat. IF your charging system does not like what's going on then you'll still have the warning sign and convenience unavailable mssg. Also on the alternator itself should have connected in the back a voltage regulator that should come with it, as some auto part places do not sell it with it but if it's bosch you should be good. Return the bat and do the job right to begin with you shouldnt have any issues! Gluck

StarvingArtist

Check the BCM in the trunk.

cetialpha5

You can post your VIN and maybe a helpful soul on here with EPC access can tell you the correct part number for the alternator. Otherwise it's $75 to sign up for a year. Used to be free, but my access expired last year. If you don't mind waiting, you can buy a $10 knock off DVD on eBay that has the WIS and EPC on it. Otherwise if it's not the alternator, then it's the battery control module as mentioned in the previous post.

There are also several online MB dealers, you can usually just send them an email with your VIN and ask them what alternator you need to buy and the price.

speedracer.eric

Just spoke with a great guy at Mercedes parts dept, he said the car takes a 14V 150amp alternator, the one I bought is 12V 150amp... can anyone verify this? Could this be the culprit?

cetialpha5

Hard for anyone to verify it if you don't post your VIN. But it's one of a couple of possibilities. There have been other threads which mentioned this same problem, there's a few alternators which might fit and using the VIN is the only way to know for sure. It could also be the battery control module.

speedracer.eric

WDBUF65J93A164722 VIN

konigstiger

OEM part is 0131548202 14V/150A.

speedracer.eric

Thank you for looking that up!
So do y'all think the 12v that I bought at O'Reilly will bolt on but doesn't put out 14v so will cause me issues?

konigstiger

New batteries and alternator, next components to check belt & pulleys if fine consider replacing alternator to OEM – definitive diagnose have someone with MB DAS (diagnostic system) check for fault codes.

cMazara

Lmao, this made my night.

speedracer.eric

OK so I've been using the live voltage readout on the speedometer;
When I start the car and let it sit at idle RPM (about 800 RPM) voltage readout = 13.8-14.0V
When I begin driving, the voltage started to slowly go down. As I got on the highway and really gave it some gas, the AC turned to low fan ("Low power, conv func disabled"), voltage dropped to 11.7-12.5 and bounced in between sporadically. I got off on my exit and came to a red light where the voltage climbed, rather quickly, back up to 13.8-14.0
Then I got on the highway on my way home from work, same issues except this time the voltage VERY sporadically climbed above 15 and back down to 12, I saw it go as high as 17V for a brief second

Please note, this is with the brand new 12V 150AMP Bosch alternator I bought at orielly auto.

StarvingArtist

That actually does sound like a bad alternator. The VR is all over the place. It might be worth taking it back and trying a different one before paying for a proper diagnosis. I don't know if the BCM can cause those symptoms or not, but the alt certainly could. I've heard of people getting several bad ones in a row from regular auto parts stores.

speedracer.eric

Well gents, it seemed to be the alternator, thankfully not a BCM. For future reference to anyone buying an alternator for this car, BE SURE it is a 14V 150AMP!

I was lucky to get a refund on the one I bought at orielly, they updated their computers that their alternator does not work for our car. Bought a refurb from mercedes, OEM $500 +$45 core

Car holds voltage above 13.5V for the most part, except for when stopped and in gear, my resting RPM is around 600 and with as much load as I could put (max AC fan, high beams, etc) the voltage dropped to 12.2 at its lowest point but didnt stay there for long, climbed back to high 12s after a moment but not above 13 until I lift my foot off the brake and raise the RPMs

AMG WORLD

See i told you, seems like all e55 owners had this problem either alternator, aux bat, main battery, or all went bad at (around) the same time. I guess there expiration date is 10-12 years!

whats gonna go bad next

EMFAudio

The alternator OReilly sold you IS compatible, it's just defective. NEVER buy an alternator from OReilly, Auto Zone, or Advance, for ANY car. They're all reman garbage (and some new garbage). Mercedes aren't magical cars, they're just like any other, they aren't smart and know if it's OEM or not.

The alternator you got said 12v because it's for a 12v system (which charges at 14v). They are one in the same thing. It says 12v because there are some vehicles that use 6v systems (rare, all pre 1960's) and some vehicles that use 24v (BIG trucks). In all cases, charging voltage is higher than the system voltage (that's how it charges), more specifically 2.4v per cell, or 0.3v per volt higher than resting.

speedracer.eric

Since day 1 with new OEM alternator, vehicle occasionally idles around 500-600 RPM while waiting at a red light. This is causing the voltage to drop as low as 12V depending how long Im waiting and/or how much load (heat, headlights, etc). When this happens, the sub in the rear pops, I think it may be going bad but it definitely notices the change in voltage. I am not getting any warning lights.

Do these cars normally idle that low?
If not, where might I start looking as to the culprit of this problem

cMazara

The only time when I see a drop in my car is when the lights are on and I operate a window or lock/unlock, like in any other previous car that I've had, seems like this are priority to the system and draw all the power that it can in my opinion, but haven't had the chance to see the voltage.

As to the idle, yes, mine idles at 600..
I'll check it out later and try to post a pic about it

EMFAudio

Where are you getting the voltage reading from? Device and location.

kurtismayfield

Eric, Pay no attention to this kajtek1fella. This guy's a eunuch. Has a history of suspensions. He is a topper too. All he does is waste everyone's time. He is exasperating...you can't dodge him unless he is on suspension as he's in many forums. I think he just got back from one on benzworld's W211 forum. It was nice while lasted.


Apart from using oem electronics & engine parts from a reputable source, the nationwide retailers are fine for batteries, wipers, wax etc. just match the specifications as suggested, and memorize your VIN. It comes in very handy when you least expect it.


Oh and by the way, Welcome to the forum!


Kurtis

speedracer.eric

Just an update, this only happens BELOW 600 RPM, when I see my car idling at 500 is when this voltage drop happens. I'm not getting any errors or warnings, I'm just surprised the car allows itself to idle that low while in gear and not moving. Makes me think there could be something wrong causing the engine to idle that low on occasion.

Typically, I too have only noticed a drop like this when operating the windows, locks, exactly like you mentioned, in any previous car I've had.
However, the drop I'm currently describing happens when merely sitting at a red light, without any input from me operating windows or such. I'll have the heat on at 3 and the radio at a fairly quiet volume as well, suddenly the RPM drops below 600, I hear the sub pop and lights dim. This is occasional, not something that happens at every red light.

Turn key to position 1, ensure speedometer is displayed on screen, triple click trip button. Current voltage will now be displayed instead of speedometer.

I paid him no attention, it was obvious he wasn't being helpful.
This being my first Mercedes, I thought I could get an aftermarket part for the engine and that it should work fine as it was with my experience in other cars. As I've learned the hard way, ONLY PUT OEM into your car for important mechanical and electronic parts. As you mentioned, I could go to walmart for wipers etc, as long as the specs match. One positive I can say to the OEM parts is that they seem to have a longer life cycle than a comparable aftermarket part.

cMazara

When you mean gear, like in 1st gear?
I drops to 600 on P or N..

About that voltage drop, you deff have an electrical issue, maybe alternator or other stuff, better have that checked out as this cars are very sensitive to electrical issues and thus can have a problem with another system in the future like ignition etc..