SyHS

Few days ago my battery started to die while i was pulling into the gas station. Ended up getting a new battery then my alternator tested bad... I ended up getting a new alternator.

Just installed the alternator tonight and went on a test drive to see if it was working well

Ended up getting the red battery symbol, alternator/battery symbol, ABS light, battery conven light, brake light.... etc... I was able to manage to get home since I was only 100yards away. Once I made it to about the 50yd mark my headlights stopped working and I also noticed my brakes were completely gone. I had to use my E-Brake to slow down the car and pull into my gravel driveway. What the hell is the issue with this now?

I was reading about a fusebox under the passenger footwell, which I ended up finding. I have not pulled any of the fuses etc yet but this problem is slowly turning into a nightmare.

The battery and alternator are brand new, and I didn't even drive the car for 10m before it all started to shut down on me.

SyHS

Didn't charge the car or anything but hopped in the garage and hit the reset button to test voltage. When the car was off it was at 11.5V. When I turned the car on it went down to 11.1V. Once I started the car and gave it some gas it dropped even lower to 10.9/11.0v.

Wondering if it has nothing to do with the passenger fusebox but maybe the aux battery or BCM?

tw2

Occasionally you can be unlucky enough to get a bad new alternator. Check codes for BCM but this would be the next thing to look at. I would put the battery tester on the aux battery anyway but it isn't your main issue.

SyHS

I've had awful luck. Member on the forum sent me an OEM alternator but USPS lost the package. I said to hell with it and picked an alternator up from O'Reileys. I asked him to test it before I take it home just to make sure it was working properly. The kid working there was being a complete dick and asked me if he should test it again after it passed the first time. I wasn't in the mood so I had him test the thing 6 times before I said I think that should be enough.

What would be symptoms of a bad BCM? Volts are just so low and the car fires right up even after sitting, it just throws battery/alternator codes within 10 seconds of starting the car.

SyHS

Going to be reading up on this issue all night lol. I am looking into it more and it seems the battery that they gave to me as a replacement is much smaller than the OEM battery.... I think that could honestly be my issue.

tw2

I need a new battery, you will want to have a 850CCA AGM battery. The dealer had the best price for me for that spec but the EPC actually had a 750CCA one listed for the E55 which I did not want to get.

Still some kind of charging issue. You should have 14.4V or more. I would suggest a STAR scan, the battery control module is pretty expensive. From quick reading it sounds like it shouldn't stop the system charging.

SyHS

I might've got a gel battery instead of an AGM... Wondering if that would be the root cause of my issue.

SyHS

This is the battery the shop gave me. It's got two vents on the side. I'm starting to think this could be the issue. Car starts fine so it'll crank with the battery. Once the car gets going under load I think it starts to mess with everything else? Can't tell if it's AGM or gel. Going back there tomorrow with it to get it tested and exchange it for a 850cca AGM.

StarvingArtist

That battery sucks compared to what it is supposed to have, but that isn't your problem. Charge the battery, disconnect the alt wires and test it while the car is running. If it's still not charging, replace it. If it is working, hook it back up and get a proper scan. Then you only have to pay for the actual problem.

SyHS

test the battery with the alternator not connected? Wouldn't that not charge the battery?

SyHS

I understand what you're saying now. Had a long day/night. Will give that a shot!

SyHS

Got a new AGM 850CCA grp49 battery... Also got a new Aux battery since it was only pulling 4 cranking amps.

Issue still exists. Car is stuck at 11.9v on position 1 and when the car is on it gives me the Brake warning and battery/alternator warning. Battery is still not taking a charge. Got a scantool that I'll be using to diagnose the issue.

Pmarino

POS aftermarket alternator

LimKenny73

Lemme intro myself.
I am Kenny here from South East Asia.
W211 2009
M272.943
3.0 litre

I am having the same issue as the OP.
Changed the battery and later the alternator.
Drove home and was allright altho i felt the charge was not enough to keep the car going for too long.
Charge will never go up beyond 13.2V.

Thought it was the Intelligent Battery Controller at the negative battery terminal. Removed that wire and IBC, and used a jumper cable to connect to ground. Car can start, but cannot get a good charge.

Next was to look for the BCM (battery control module) but i cant find it. I think it is only for dual battery cars. Mine has only the DIN100 battery.

I cannot brain the issue out. Need advise here.

Tracing the wire from the battery compartment to the front came to the engine bay SAM module. I have a feeling it could be the culprit.. but it is a really expensive part to get, program and hope for the best.

Anyone with a single battery model here?

JohnLane

Check voltage at output of alternator while charging. Should be 14 volts give or take two tenths. If low... start with an alternator that works. Alternator and battery are far and away the most common problems.

juanmor40

If the voltage at the alternator is 14V+, then move to check grounds. If the engine is not grounded properly to the body (that is how the alternator is grounded), there may be a voltage drop and issues start to creep up.

LimKenny73

Thanks John.
Will give it a try, tho to be honest, this is a new alternator with 180A of juice. I believe it could be a grounding issue, but as far as i can see, all the ground wires are tight.

It just refuses to charge anything higher than 13.1 to 13.2 volts... And when the engine has warmed up, the charging voltage drops to 11.8 V..

To me, it points to a possible issue with a ECU/SAM controlled charging parameters.

Never encountered this problem in my other rides before.

Oh btw, i had a 2.5 engine which i swapped to this current 3.0 with full overhaul (short of reboring the cylinder well) .. Total cost is more than the car is worth.

Also, I tried to switch the front SAM unit with the original SAM from the 2.5 litre engine. The key just stayed jammed in 0 position. Looks like i need to program it to match the 3.0.. Sighhhh...

Crossing my fingers 🤞🏼🤞🏼

juanmor40

Careful here. Tight ground cables is NOT what I suggest. With checking ground in these cars I mean, lose the connection, CLEAN the contact as best as you can, Apply some kind of oxide protection, say Deoxite, tighten the connection back.

Ground checks --> Reduce electrical contact resistance at the connection.

LimKenny73

Ok, so after a week having the issue resolved, i am confident to inform that we have fixed the issue.

It is Pre-Fuse F-32 which is the connection point between the alternator and battery. There is a capacitor there.

My gut feeling told me it was the problem as the original alternator was charging 150A and the new alternator is charging 180A (M25 to M30 engine).. the workshop did not change this Pre-fuse and was still running on the old unit. My guess is the capacitor was not meant to deal with higher amp, and gave up after a while. After changing to the original M30 pre-fuse, the alternator charging has been a healthy 14.1V and all the electricals are running like a dream.

Thanks to all who shared their thoughts on this problem.

Learning something new everyday about my W211...

nd-photo.nl

@LimKenny73 I think I have a similar issue, I checked the specs of my alternator and its also a 180A alternator. I found this video, which shows 2 fuses (around 1:15 mark). Did you replace them both?


[edit]
Also found this document about the dual battery system with pictures of F32 etc

LimKenny73

Hi. To clarify, my W211 is the facelifted, single battery model without the auxillary battery. This is quite rare where I am (i mean for a 2.5 litre engine)...

But the problem was this F32 pre-fuse unit. The workshop did not replace any fuses, just the entire pre-fuse unit direct. Also made sure all the fuses were intact before swapping.

I believe it is the capacitor problem.. In that it could not hold the charge from the alternator.

Having said that, i will have a look at my old unit to see if there is any burnt 150A fuses as well.

Will send you a pix later.

nd-photo.nl

I wanted to check this weekend, but I didnt know you need to loosen a nut under the car to remove F32. So I only cleaned & scuffed the contact points, I did the same with the BCM