W211 Charging woes

[fisheggs]

Hi All.

2003 W211 E320cdi.

I've recently been getting the convenience functions disabled warning.

I had both batteries checked and they were both ok but required charging. I pulled up the voltage display on the instrument cluster.

Heres what I found.

In the morning or first startup of the day , prior to starting, the voltage is 11.9 ish, once started after a few seconds, the voltage will shoot to 13.8/9 and will stay around this area for a while. Whilst driving and engine temp increasing whilst idling in traffic etc, the voltage will slowly drop from the 13s down to 12 and late 11s.

So it is charging 1st thing but as temp increases, charging drops off. I have checked with a voltmeter and found similar readings.

I have removed and cleaned battery terminals and earth point in boot.

I am thinking voltage regulator or BCM although vehicle appears to have original batteries. I called up MB and some sort of recall or workshop procedure was carried out to the charging system in 2005.

I don't want to guess a part so I'd appreciate experienced forum wisdom

 

[BlackC55]

You need it on a Star firstly. This can check the BCM.

I would say that the alternator is on its way out.

 

[fisheggs]

Cool, Thanks!

WIll get to a star machine first. In the meantime, Does the alternator have to come out on a 320cdi or can it be done in situ?

Also, any OE part numbers?

Thanks

 

[BlackC55]

To replace the alternator it does have to be removed. Its a bit tight on that engine. I usually end up unbolting the engine mounts and lifting the engine up.

Get the alternator from Euro Car Parts. Just quote them the reg on the phone and they will look it up for you. There are two variants IIRC.

 

[fisheggs]

Thanks

Just wanted to update. After reading a few other threads on this subject, I decided to change the voltage regulator on the alternator. £50 from MB and installed pretty easily in a couple of hours.

Showing a consistent 13.9v when driving and not dropping off when hot.

 

[BlackC55]

Great result!

We tend to replace the alternators as we do get a few that suffer from worn bearings too.