W203 2004 C-Class Battery alternator warning. Jump start fried something?

[Kaz073]

Greetings.
I've been tolerating this red warning light over the last 4 years. First time i witnessed it was soon after AA man jump started the car after I clumsily left the keys in the ignition overnight and drained the battery.

So I replaced the original Mercedes battery with a Yuasa from Halfords. All good for 6 months until a bearing went on the alternator and the warning light would show.. and rightly so. So splashed out a new Bosch alternator.

Couple of months later to my surprise the red warning light showed again. I ignored it thinking it was a one off. But come the winter time the light was back, most usually on cold mornings after sitting overnight. The car would always start though, so the alternator must have been charging. I eventually took it to the garage that fitted the alternator and they tested it and the battery and said everything was fine and to come back if the light would show again. It didn't ..as the weather was warming up that time..this warning was sensitive to cold temperatures. The light would be back next winter..
but i was too busy to get it checked out by the garage. And so the two year warranty on the alternator expires. I did get the battery replaced under warranty, but no help.

Now this darn light shows up on almost every start regardless of temperature and sitting time. And now it sometimes flashes several times while driving. I'm afraid now something is going to give and leave me stranded.

I've used a scanner...getting a P0620 code - Alternator Control circuit malfunction.

As I saw the red light first time soon after AA man jump started the car...im wondering if the problem stemmed from that. I distinctly remember him jumping straight to the battery terminals and didn't use the dedicated charge ports. Did he fry something? I really can't see it being a faulty alternator given that it appears to be still charging.

Please any help or suggestions
Thanks.

 

[Tony Dyson]

Greetings.
I've been tolerating this red warning light over the last 4 years. First time i witnessed it was soon after AA man jump started the car after I clumsily left the keys in the ignition overnight and drained the battery.

So I replaced the original Mercedes battery with a Yuasa from Halfords. All good for 6 months until a bearing went on the alternator and the warning light would show.. and rightly so. So splashed out a new Bosch alternator.

Couple of months later to my surprise the red warning light showed again. I ignored it thinking it was a one off. But come the winter time the light was back, most usually on cold mornings after sitting overnight. The car would always start though, so the alternator must have been charging. I eventually took it to the garage that fitted the alternator and they tested it and the battery and said everything was fine and to come back if the light would show again. It didn't ..as the weather was warming up that time..this warning was sensitive to cold temperatures. The light would be back next winter..
but i was too busy to get it checked out by the garage. And so the two year warranty on the alternator expires. I did get the battery replaced under warranty, but no help.

Now this darn light shows up on almost every start regardless of temperature and sitting time. And now it sometimes flashes several times while driving. I'm afraid now something is going to give and leave me stranded.

I've used a scanner...getting a P0620 code - Alternator Control circuit malfunction.

As I saw the red light first time soon after AA man jump started the car...im wondering if the problem stemmed from that. I distinctly remember him jumping straight to the battery terminals and didn't use the dedicated charge ports. Did he fry something? I really can't see it being a faulty alternator given that it appears to be still charging.

Please any help or suggestions
Thanks.

One of the reasons why jump start points are located remote from the battery and in particular the negative connection is directly connected to the chassis and not the negative post on the battery is the potential damage that the EBS (Electronic Battery Sensor) can suffer during a mismanaged jump start.
The EBS is a key component in electrical energy management of a car and it's functions will vary on different models, it is the small black box attached to the negative battery post about he size of a small matchbox with a pair of control wires attached.
As you've had the alternator and battery checked, I would suggest to have someone further diagnose the EBS who is more familiar with your car model.

 

[mersum1es]

Measure drain current when car is standstill. That will cause you battery drop overnight. Then you might have 'wrong' type voltage regulator, car is charging but at constant 14.3V, and this triggers fault code. AFAIK no separate battery control module in W203.

 

[mattkh]

I dont have a C180 W203/2004
If possible, please put up a picture of the electrical connector going into the alternator, the one with a few thin wires.

 

[Kaz073]

Thanks for the replies.

- Tony Dyson, i checked for an EBS and it appears this car doesn't have one.

- Mattkh.. wish I could take a photo, but getting under the car and removing engine undertrays to view is beyond my capabilities at the moment. Do you think a wire has been damaged somehow?

-mersum1es, you could be onto something about the voltage regulator being the 'wrong type'. I've read somewhere that these cars can be very picky with which alternator has been installed. im assuming the VR comes included with new alternators like the Bosch i had installed.

Anyway, I took the car for a spin today in the good weather and before setting off I had the voltage reading on display. Engine off, reading was 12.2 v. After start, reading had risen to 14.0 v almost straight away. 10 seconds or so later dreaded red warning light displays, reading still at 14.0 v. Normal driving voltage hovers around 14.0 v. Idling in traffic it drops to around 13.5v. But today I noticed it had spiked to 15.3 v while driving after 3-4 minutes or so after start..then a few seconds later 'light sensor drive to workshop!' yellow warning appears on dash. Checked voltage reading still around 15.3 v...then a few seconds later 'coolant visit workshop!' yeĺlow warning appears, i cancel and check voltage..still holding at 15.3 v. I pull over fearing something might break. i restart the car and drive....voltage hovering around 14.0/1 v. and remains so for the rest of the drive and back. Now ive seen both these warnings before...the light sensor one, usually after i haven't driven the car much after a couple of weeks or more .The coolant one ive noticed a handful of times in recent years. ive just topped up with a bit of coolant assuming its something to do with level. But i think its telling that both these warnings appeared togther in conjunction with the 15.3 v spike!

So its looking like a problem with the voltage regulator? Or perhaps theres an issue with the wiring? I just hope im not told to change the alternator or battery again.

 

[DREAMER NO2]

Important that if owners are not sure on the right way to jump start a Mercedes is to leave well alone . I rule of thumb never jump start your Mercedes .

 

[mattkh]

- Mattkh.. wish I could take a photo, but getting under the car and removing engine undertrays to view is beyond my capabilities at the moment.

I understand, some cars have them at very awkward places.

 

[mattkh]

..... im assuming the VR comes included with new alternators like the Bosch i had installed.

Yes. The VR is part of the Bosch alternator.

 

[mattkh]

......I've read somewhere that these cars can be very picky with which alternator has been installed.

If possible, check with the garage that installed the alternator whether they told the car's ECU which type of alternator they had put in OR
was it plug and play.

 

[mersum1es]

There is no such option either, either is correct VR or not. It communicates right or not. True, it depends on engine ECU what is communication route with alternator- these models are supprted for DAS generator test if there is LIN or BSS:
111 PMS, HFM, ME2.0 TRADITIONAL (if no communication port)
112, 113, 155 ME2.8 TRADITIONAL (if no communication port)
137 ME2.7 TRADITIONAL (if no communication port)
166 MSM TRADITIONAL (if no communication port)
266 SIM266 LIN
271 SIM4 BSS
272, 273 ME9.7 LIN
275 ME2.7.1 TRADITIONAL (BSS generator, MSG not supported)
275 ME2.7.2 LIN
285 ME2.7.1 TRADITIONAL (BSS generator, MSG not supported)
611, 612, 613 CDI TRADITIONAL (if no communication port)
628 CDI V1 TRADITIONAL (BSS generator, MSG not supported)
629 CDI 5 LIN
640 CDI A LIN
642 CDI 4 LIN
646 CDI 3 TRADITIONAL (if no communication port)
646 CDI 3 (UP) BSS
647 CDI 4 TRADITIONAL (if no communication port)
648 CDI 3 (UP) BSS
668 CDI TRADITIONAL (if no communication port)

 

[Kaz073]

Is it a case of just swapping the VR out for a fully compatible module or does the alternator unit have to be changed as well? I think my next step is to change the VR and make sure its compatible. How can i be sure im purchasing a compatible VR?

 

[alexanderfoti]

You can swap out the VR. id look up the MB part number of the alternator and cross ref against a bosch number to get the right VR

 

[Uncle Benz]

In my workshop this week...

I’ll start by apologising, I didn’t take any photos... I had the pleasure of a very tidy S203 estate with an m271 engine this week. 58k on her, and very well kept. The owner is the father of one of my long time customers. The car came to me with some history and work carried out elsewhere. There...

forums.mercedesclub.org.uk

 

[Uncle Benz]

Been there, got the tee shirt

 

[alexanderfoti]

Swapping the VR should sort that ^

 

[Uncle Benz]

Swapping the VR should sort that ^

I believe you really need to make sure you fit an alternator that matches the original, Bosch or Valeo. They fitted both types at the factory, and I think there can be a compatibility issue if you mix them up. I detailed this in my other thread

 

[Uncle Benz]

To the OP. Buy a service-exchange alternator from Mercedes to your chassis number. I’m sure it will resolve your problem.

 

[Kaz073]

I

I believe you really need to make sure you fit an alternator that matches the original, Bosch or Valeo. They fitted both types at the factory, and I think there can be a compatibility issue if you mix them up. I detailed this in my other thread

if thats the case, i think i might buy a used unit from ebay

 

[Kaz073]

To the OP. Buy a service-exchange alternator from Mercedes to your chassis number. I’m sure it will resolve your problem.

thanks. i'll look into this. if i manage to get hold of one and fit it, i'll report back with findings.

 

[Uncle Benz]

thanks. i'll look into this. if i manage to get hold of one and fit it, i'll report back with findings.

Definitely worth enquiring with Mercedes first. Parts department will tell you if it had a Bosch or Valeo unit originally.