W211 - New alternator? Or Battery Control Module?

[XPS420]

I have a '03 W211 320 CDI. Past 2 days its been giving error code of, "Electrical Consumers Switched off" This error was at random when i was parked outside a friends house. Then today it was giving an error of "Battery/Alternator Visit Workshop" ( or something like that ).

So i took my voltmeter out and tested the battery. With the car Switched OFF(engine not running) it makes 11.70v Which is LOW. Then with the car Switched ON(Engine running) it makes 11.20/11.19 volts. This voltage has dropped since the last 2 days. it was 11.70 then i been measing it and its just going down and down while the car is running.

I took it for Diagnosis and guy said it could alternator after he checked the charging voltage and said it seems abit low. Fair enough i need a new alternator.

But could it be the Battery Control Module as i've been reading on the forums and found a Few 2003 W211s to be having these issues...? Is there anyway i can tell the Battery Control Module is bad?

Any help?

 

[SavMan]

Where are you taking the reading from when the igntion is running?
Try checking at the jump posts under the bonnet. If this is normal reading and higher than at the battery itself then it could be as simple as a corroded earth lead, check the one from the battery to chassis first and work your way through. The alternative is to get the car on star which any good indie can do for you for a small fee.

 

[XPS420]

I'm taking the reading directly from the battery in the boot.

 

[Alps]

theres a regulator on the alternator that can be replaced, dont spend money on a whole new alternator, its either that or the battery control module, regulator is around £70ish

 

[SavMan]

I'm taking the reading directly from the battery in the boot.

Take a quick test at the battery posts, I had a similar issue and was told it was likely to be the alternator but when I took a reading at the jump posts under the bonnet it was 14 volts. After checking the earth connection from the battery to the chassis and cleaning the reading at the posts read 14 as well.
However the chances are that the regulator or the control module is the culprit but as you have a multimeter checking if there is voltage drop is relatively easy.

 

[Troon]

Don't forget that pre-facelift 211s have two batteries - there's a small auxiliary battery under the bonnet.

 

[XPS420]

Why would the battery show a lower voltage when the car is switched on, it seems that the battery is being drained once the car is switched on??
Also some people talk about Water cooled alternator. Does my car have this? And i need the part number for it. Where on the alternator can i find this as im planning on looking for the part number on the alternator. and if possibly remove it from the vehicle.

i am mega confused..

 

[Alps]

you are right prob not battery as voltage is low when car is on, most probably regulator on the alternator, but need to check voltage at alternator to see if it is that.

 

[XPS420]

Where can I purchase the voltage regulators? I been to camberly auto factors as they said they do it, but the guy couldn't fin one for my at.

Where else can I look?

 

[BlackC55]

Where can I purchase the voltage regulators? I been to camberly auto factors as they said they do it, but the guy couldn't fin one for my at.

Where else can I look?

Get one from MB. They are not expensive at all and often in stock.

 

[XPS420]

OMFG!! I spent over 4 hours trying to wiggle the alternator out? How the ****ing **** do i take the alternator out of that crazy ass small gap? I know others have done it but how!! The only thing i can think of is [ANGLE GRINDER] lol

At one point i felt like killing a everyone near me or setting the car on fire, its ****ing crazy! i spent all the day on this darn thing! and still wasn't succesfull. Been on the floor under a car all day long! my back, neck and arms are hurting bad and i still got to do it to remove it.

What am i doing wrong.

RAGE!!

 

[XPS420]

ok i manage to get it out in the end, and manage to shove new one in. IT went in pretty easy for some reason. lol

anyhow bolted it back on connected it all up, put on undertrays and job done. tested voltage at battery and it was showing it is charging the battery at 13.5v bearing in mind the battery it self is 11.2v at the moment so after a bit of driving i will check the voltage again. But all the errors related to this fault are gone thankfully. and i have calmed down abit.

 

[hazee]

Where are you taking the reading from when the igntion is running?
Try checking at the jump posts under the bonnet.

Where are the jump posts under the bonnet of w211 2004 to check the voltage?

 

[mersum1es]

Where are the jump posts under the bonnet of w211 2004 to check the voltage?

Sedan has none. Estate should have similar than W210 (match box size black box, pobably '+' sign on it).

 

[hazee]

Sedan has none. Estate should have similar than W210 (match box size black box, pobably '+' sign on it).

Then how and where should I check the voltage to know if the problem is with the voltage regulator or battery?