Battery aternator visit workshop

[philv]

Hi

Mercedes b180 cdi auto.
2006.

Bought car used.

ater a ew days the car battery went flat when not used for a day.
GEM got the car charged again.
But engine check light stayed on.

So got Battery replaced....all fine.

A week later...tonight the message pops up-
battery
alternator
visit workshop

It is a general battery/alternator/charging message.

But i am assuming it is the alternator.

But is it odd that there was no message before?
Or is it possible previous owner turned the message off?

I would have thought the message would have been popping up before the battery died?

[philv]

The voltage is around 11.6 with engine running.
12 with engine off.

[AdamIndy]

It should be 13v+ with the engine running. Either something wrong with the charging circuit or the alternator is knackered.

[daveenty]

Usually the regulator on a Merc, which I believe can be sourced independently of the alternator.

As stated above, should be > 13 volts when running, nearer to 14 really.

[philv]

Is replacing the regulator a standard garage job?
Or does it require a specialist?

[daveenty]

Most auto electricians should be able to sort it, though I would be tempted to take it to an MB specialist to confirm it is the regulator which is needed.

Diagnosis by internet is no necessarily a good thing.

[996TT02]

Can't specifically advise re the Merc but on some alternators the regulator is simply removable from the alternator, a simple job (access permitting).

[philv]

As it is a bosch alternator.....would any boschesupplier eb abel to get it?

Or get it fixed via bosche service centre?

[philv]

If it is 12v engine off and 11.5v engine running.
And the battery/alternator/visit workshop light comes on.

Does that mean that the alternatorr is doing nothing and the battery will be flat in a couple of days running?

Or is it still doing something and ok to drive till fixed in a week or so?

[PhillipM]

It's doing nothing, 12v is an almost flat battery to start with. Get it on charge before you kill another battery.

A good alternator is usually 14.4-14.7v when running, and default mode for most of the PCM controlled units even with a goosed regulator is usually at least 13v.

[philv]

Must admit to being a little confused.
It seems that tne alternator not charging probably meant tne last battery died.

But it is a week later before a problem comes up after the new battery.

Is that badically a week of starting tne engine?
The battery would not have been used for anything else but engine starts.
And that is tne reason it took a week for tne problem to reoccur?

[PhillipM]

The battery will be used for everything given that voltage level - the alternator is doing nothing unless it's self exciting further up the rpm range and you have a wiring/field coil issue - it's probably just the battery was big enough to last. But to be honest discharging it to 11.5v when running will not have done it any good at all.

Edited by PhillipM on Sunday 14th February 21:35

[powerstroke]

philv said:

Must admit to being a little confused.
It seems that tne alternator not charging probably meant tne last battery died.

But it is a week later before a problem comes up after the new battery.

Is that badically a week of starting tne engine?
The battery would not have been used for anything else but engine starts.
And that is tne reason it took a week for tne problem to reoccur?

Yes The battery is a store of energy the altenator replaces power used to start and run the car
its possible the alternator was working allittle bit enough to put the warning light out
but not enough to keep the battery fully charged , as others said fully charged battery about 12.5 volts , engine running should see about 14v