Celicasaur

Driving this evening thinking how well behaved the car has been over the last month and that I'll treat it to a nice pulley and tune....then the red battery message comes up again!

Since xmas I have fitted:
New Bosch rear battery
New Bosch front battery
New MB rear BCM
New MB front BCM
New MB alt brush pack
Reconditioned original alternator

lol i've revamped the entire charging system!!!

I'm guessing it's going to be my front BCM....again! I checked voltage at the rear and at idle it's running very strong at a steady ~14.00+ (it's not even in the 13's anymore). It can't be either of the batteries, nor will it have anything to do with the rear BCM, alternator or brush pack (because the battery voltage wouldn't be showing and so good)

I have to ask....can anybody think of a way/reason why I would be blowing through these front BCM's? My original one was changed in Aug last year, then I replaced it again in December...this is the third one in 6 months and it's getting expensive to continually buy these. Any reason why these would be blowing out?

Viet_Amg408

red battery message usually cause by alternator not producing current to cancel out reference voltage from BCM.

Have a second look at the alternator again..

urbamworm

The voltage regulator, not sure if that is what you are calling the "brush pack" or not was the problem in my car. Red battery, visit workshop popped up and conveniences disabled. I put the center display to voltage reading and it was reading upper 13s at one point then 11 at another point. I drove the car 2 miles and it went away. I had the car at house and started it and it was like 13.7 during one test. Ended up changing the voltage regulator on back of alternator and it fixed it. The 2 spring loaded leads were worn down some compared to the new one I was installing.

Quadrobenz

Here is another possibility to consider. I got the red screen accompanied by no brakes a couple of months ago on my SL600. Depending on the year I am told these are virtually identical systems to the E55. I had the car flatbeded to MBLN. All the components in the system tested ok. The fix was a software update MB recently certified and released for use.
I understand there were a large number of brake failures in the dual battery cars with no equipment failures that drove MB to research and rewrite the software for the controller. My SA was not aware of the software update until my car came in.

novae500

Culprit may be the reconditioned alternator.

1970gsx

My buddy was having the red battery message in his '06. After replacing a lot of stuff, it ended up being an inline fuse in the charging wire harness. His mechanic replaced the fuse( he had to tear into the harness as a new one was $500, fuse was $6), and all is good now.

Brabus K8

Changed my alternator beginning of this month after red lights, problem solved, no issue with new alternator. LIGHTS GONE, thank God.

urbamworm

It was probably only the voltage regulator on the back of the alternator, not the actual alternator that was bad. About 20 minutes to change it and under $100 for the part.

berti_00

that stupid Voltage Regulator can cause some major issues... i had to replace mine twice. my lights in the interior were diming on idle

skratch77

I think I might need a new regulator and what is a bmc module and where is that inline charging fuse?

My car sat for a few month with a tricle charger and I get the red warning right when I start the car,on the dash I get 12 volts with the car on and 12.1-12.2 with the car off.

If the main rear battery is bad can the system detect a bad cell and stop the alternator from charging it?

Celicasaur

Thanks guys

With all this battery misfortune, I'm almost an expert on ghetto diagnosis.

Right, when the car if on, if your voltage is in the low 13's, then a simple replacement of the voltage regulator (lol sorry Urbam, no idea why I called them brush packs - it's a British thing) - I did that on my car and it's showing a strong 14+, which it never did before. If/when your rear battery gets voltage, that means the alternator and rear BCM are operating just fine. Also, if your alternator or voltage regulator are not working, then your rear battery will not be charging (not even in the 13's) and eventually you will get SBC warnings and a constant beeping sound telling you to stop and do something before the car totally shuts down and causes an accident. Furthermore, when you put the key in the ignition and turn (but not start the engine) you will NOT get the red warning light. That'll only come on once the engine is started and it realises there is no charge.

On the contrary, if you turn the key (not turning the engine on though) and the red light comes on right away, that means it's a problem with the aux battery relay under the front wiper cowl. This isn't detrimental to the car like the rear battery not charging, but it will just **** you off because it's annoying and you'll want to fix it. I think I might try the firmware update idea though....maybe that might be what's blowing them for me. I need to figure out why they're blowing though because these things are not cheap

Finally, if you're having SBC-stop related issues (car doesn't stop by itself when you press downward on the cruise stalk) and it says SBC not available (in the small writing, not big writing) then that means combination of either your front aux battery going bad or your front aux relay is going bad.

It's sad that I know this, but that's what you pick up from having so many damn electrical gremlins as I have

novae500

I went through this last year. Very frustrating!!!

skratch77

I think my voltage reglulator is bad,are there any fuses to check?I charged the battery to about 12.4 volts and it starts the car just fine and the second it running I get the red dash and the voltage is 12.2 volts and drops when I rev it.

saleen01

How do you know what a bad voltage regulator looks like and do you have a part number?
thanks

urbamworm

Like mentioned above, you will see lower voltage readings if you toggle to voltage in your center display, possibly low 13s instead of 14, or you may have something lower at one point then higher at another point.

You won't really know unless you take it out if it is bad/worn. In this pic the one on top is new and the bottom is one that was giving me trouble. You can see those 2 prongs facing inward near each other from both voltage regulators in center of pic touching the other voltage regulator (there are actually 2 on each voltage regulator, you just can't see the 2nd one on each since it is below the one you see) and see how the one on top has longer prong that actually touched the housing of the bottom one but the prong on the bottom one doesnt quite reach up to the top one? Those get worn down and don't make good contact all the time and cause for the fluctuation in voltage.

Celicasaur

Sounds like your alternator bro.

But by all means remove the voltage regulator first. What you'll find though is a gradual loss of voltage if it's the regulator. If I were you, I'd remove the alternator and take it to a shop for testing. It won't cost much and tbh if the alternator is fine, then the only culprit it could be is the rear BCM.