Hello guys,

So suddenly I got this "undervoltage consumer defective" warning in my dash.
I figured probably it's the generator/voltage regulator or something as my battery is like 1 year old.

But I was wondering if there was any way to make sure of this? When I measure on the battery while the engine is running, the voltage just drops slowly on my battery. It was like 11.97V before I started the engine, and then it went up to like 13.5V when I started the engine. And then slowly made it's way down/dropped to 13V in, let's say a little more than 5 minutes.

But I remember when my battery was bad, it behaved the exact same way. So it could might as well be a bad battery that isn't picking up the charge from the generator, as well as a bad generator..?

And according to this thread, also a bad ground return... Which I am going to test myself when I get to my car again. https://mbworld.org/forums/c32-amg-c...ator-help.html


Do I need STAR to do a proper generator test anyway? The price for a new generator here in Norway was actually a lot (the 120A one), so I really don't want to buy a new one just for testing.

 

It appears that the alternator is charging and the battery also seems good, especially since you appear to be able to start the engine.
I just went through something similar and it was the voltage regulator, which was inexpensive.
My charging voltage was 13.6 and 11.8 when off, but it would completely drain the battery overnight, as the VR had a parasitic drain, so I replaced it.

I know this doesn't answer your issue, my point is that the alternator might not need to be replaced.

The dasboard message almost points towards a device that drains the battery. Can you change the language to German and see if the original message is clearer? It looks like the English translations were done using an online tool...

Unless someone else on this forum has a better idea...

 

I recently charged the battery up, and the battery was like 13,1v or something. Started the engine, battery went up to like 13,6v, and then just started draining slowly down from there while the engine was running...

If someone revved the engine, the draining would stop, but it would Just stay still.

The charging/battery was at 13,2v when I stopped the engine. Measuring the battery afterwards, it is 12,85v. (when not running)

But it seems to be a charging issue, as it is slowly draining while the engine is running.

I tried to add a ground Wire from the chassis to an engine bolt/screw, but didn't seem to do any good.

The battery doesn't seem to be draining when the engine is off. It stays at around 12,85v.

But I am still not sure what part that is faulty.

 

I'd try a new voltage regulator and see if that solves it.
Since you have confirmed that it's not a ground issue, it's either the alternator or the regulator. I think the alternator itself is fine - see the initial 13.6v, if it was shorted I doubt you'd get any charging at all...

 

Yea but the charging is not stable at 13,6v. It just started there with a fully charged battery, and went slowly down from there. Seems weird.

But is it common that it is shorted? Can't it just be a bad alternator in that case?

Can the regulator cause this behavior?

 

Look at it this way: the alternator is pushing current into the battery, and the car consumers are pulling current from it. Current x battery resistance = voltage on the battery terminals. If there was no charging, the battery would quickly drop to 11s (i.e. total negative current flow). Since it is sitting at 13.x, we can assume the alternator is supplying just a bit more current than the car is pulling, and that is going to the battery, so voltage is not dropping too low.

You can test the regulator (search in google) to be sure what is causing this. I believe the alternator itself is unlikely to fail though.
Can you get a remanufactured alternator? They cost ~$150-200 in USA.

 

When I called around different stores here in Norway, they were talking around 1,000 USD for a Bosch 120A alternator for this car. And if I returned the old one I could get it a little bit cheaper. I found some alternators that was cheaper here in Norway, but I have no idea what brand it is..

But I started checking eBay, and found this for example: http://www.ebay.com/itm/LICHTMASCHIN...EAAOSwv-NWUGwj

I have no idea what brand this is though, and if it is any good.

I found this, but is this an original bosch alternator? Since it was so much cheaper than here in Norway.. http://www.buycarparts.co.uk/bosch/1158782

 

Any re-builders in your area?

 

I don't think so, but it would probably cost a lot here for the time to rebuild anyway.

 

Just curious, would it be normal for the alternator to die out this early? The car has only ran around 173,000 km. A little over 100k miles.

Wouldn't it be more likely for the brushes to be worn out? And the brushes are part of the voltage regulator if I'm not mistaken?

 

That's what I've been telling you - voltage regulator is more likely to be the issue.
The car is 15+ years old, things start to wear out from age as well as mileage.

FIY, last time I checked it was pretty easy to tell Bosch from Valeo alternators - the cooling openings are different on them.
Is your engine M271? I'd replace the whole alt then. Otherwise you are looking at replacing its overrun pulley soon.
Not really sure what they do when remanufacturing the alternators - probably they just replace the pulley and voltage regulator anyway

 

Yea I wonder what they do too when they remanufacture them..

No I think it is a m111. I have the 2000/2001 w203 c200k (203.045). 4cyl, 1998cm3

But is there a lot of difference between the alternators? Do I have to remove mine to check it and make sure I order the right one? When I run my license plate through the systems I only see that I need an 120a one. But I read somewhere that the pulleys can be different, and also the power plug on the back can be a bit tricky because of the space, on one of the alternators. But it should work with both. (Atleast for bosch/valeo). Except for the pulley, but maybe that is only when stores have sent the wrong alternator, I know I read that here somewhere.

 

You are spending too much time discussing the issue.

Did you find out EXACTLY what the message in the dashboard means?

Did you try any troubleshooting to isolate the culprit, such as pulling fuses one by one?

Did you identify the make of the alternator, in case you Do need to replace it or the VR?

Sorry if I appear harsh, but you need more info to get to the bottom of this.

 

The message in the dashboard means that some electrical parts are getting undervoltage from the battery? Which I thought was because the battery is slowly draining because it is not getting good enough charge from the alternator? Which at some point would leave the battery below 12V or whenever this message kicks in.

I haven't tried pulling any fuses, no. To find out if anything is draining the battery? When off, the drain on the battery is 0,6-0,7Amps. But maybe it needs to sit a bit longer for everything to go to sleep. But of course as you say, there could be something that is dramatically draining my battery when the engine is running. But I don't know which fuses to try, and what I could try to pull when the engine is running. If I could harm anything by just pulling random fuses when the engine is running.

Imo it seems like just the charging is bad, either caused by the voltage regulator or the alternator as people have said earlier in this thread. When I started up my car now today, it actually started at 13.9V again, but went all the way down to like 13.2V after a couple of minutes, and even further if I turned on headlights, AC full etc.

I can't identify the make of the alternator without completely removing it, no. Because of it's location, and it's probably old so the text is very bad.

I could of course just remove it to check, but it's twice the work, because I would need to put it back again to use the car. If not, it would stay in the garage for a long time until the new part would arrive here. Especially if I'm ordering from outside the country.

That's why I was asking here what could be the problem/what usually occurs. And if the 120A alternators for this car was very different, or if they are the same anyway. For example the bosch/valeo etc.

I am just trying to find out if it would be the alternator itself, or the brushes/VR or the pulley. If someone had experience from this. And I have received answers and good help/tips, so thank you all for that

 

Well, if it helps, mine also starts charging high, at about 14.2V then quickly drops to 13.6, even 13.2 V
I have a digital gauge connected to the Can bus at all times and it can monitor up to 4 parameters.
So when idling it can drop to 13.2 and no errors are shown.

You are right that it's hard to know which fuses to pull when the engine is running, but there should be a diagram in the fuse panel to the left of the dasboard.

It might help starting with the usual suspects: power seats, seat warmers, audio system, try the forums for more components that are problem-prone.
Or pull everything unessential, one at a time so the fuses don't get mixed up. Then start the engine (the message comes up when you start it, right?) and hope for the best.

It just occured to me that the fault may have been stored. Do you have any means of reading the codes and resetting them?

And afaik, there are Bosch and Valeo units on the W203 so that makes a difference when ordering parts. Bosch regulators are about a third of the price of a Valeo regulator, at least at Autopartsway.

 

Yea I will check this when I get home in a couple of days. But the error is not showing up when I start, no. Because I charged the battery up, so it is still on the good side. But it is probably soon down to the error again. It usually happens after I drive a few kilometers, (this was before I charged the battery). I have not received the error after I charged up the battery, but I have only driven around 10km after that. And I can see the battery has been a bit drained after that.

 

Diodes.. If ur vr is bad, your voltage will be high if ur on the throttle because there is nothing regulating it,typically.... Diodes in the alternator easily cause parasitic drains. Try putting ur multimeter inline with the ground . let the car sit and "go to sleep". Then unhook your alternator and read the multimeter and compare.

 

Okey I took a look at the car today. Didn't make any difference when disconnecting the alternator wire. I also removed the regulator to have a look at it. The brushes didn't look that bad. They were like 7-8mm and 10mm. It was indeed a bosch unit.

​​I was hoping to only replace the regulator, because the alternator is kinda trapped in there. The guides I looked at, seemed a bit different than how it was in my car. So I tried to pull it from underneath, but then the PS pipe is in the way.. Only missing a few millimeters to get it out.. Been trying to bend/push the pipe away, but I am trying to be careful aswell, bc I don't want to damage it either. Pulling it out from the upside seemed very tight...

 

I had a similar problem a few years back. A bad VR makes the other systems do funny things. It wasn't mentioned in the linked thread but I did also have an alternator warning every one in a while when I had this problem.

It's honestly the cheapest fix at this point. If I had known this I wouldn't have wasted money on a new battery.

 

Yea it is a lot cheaper indeed if you compare it to a new proper original alternator..

I think I'll try order one to try. I have not been able to set off time lately, because of packing and moving to another house. The car have just been standing jacked up in the garage...

But it seems that it is not charging at all. It is probably just running on the battery until it has drained below 12V. And then I have to charge the battery up again myself. Dunno if the VR can cause the alternator to not charge, but I guess it can do funny things as you say. Like trick the alternator to think that the battery has enough volts, and doesn't need any charging or something..

 

Update... I replaced the voltage regulator , but it did not help much. It actually got a little bit better , as it now seems to be charging when revving the engine . But nothing when the car is just standing still with no revving. Around 2-3k rpm it starts to charge "acceptable" .


Guess I have to replace the whole alternator then ?