I have a 2007 SL500. Two days ago I got a red message where the speedometer is. It showed a picture of the battery and it said Visit Workshop.


I did some thorough tests this morning and I also replaced the front battery yesterday. Here are the results of the testing done this morning:


1) Before running any tests this morning I checked the rear and front battery voltages and came up with front battery voltage (new battery) of 12.85 and a rear battery voltage of 12.73.
2) Then I started the engine and the front battery voltage was 14.19, although it slowly variated between 14.16 and 14.23 volts while the engine was running. The rear voltage when the engine started went to 13.95.
3) Within a minute or so, with the engine still running, the rear voltage started slowly dropping from the 13.95 to 12.24 where it stabilized, yet the front voltage remained at 14.16 to 14.23.
4) When the battery symbol and visit workshop message came on during the testing the front battery voltage dropped to 13.25 and the rear battery remained at 12.24.
5) I shut off the engine a let the car sit for 20 minutes or so and then checked the battery voltages again and the front battery showed 12.85 and the rear voltage was at 12.57.


Because of the voltages when the engine was started it told me the alternator was working and even though the front voltage dropped to 13.25 when the battery message came up it still told me the alternator was putting out although it's voltage drop was kinda weird. And, as far as the lower voltage reading (13.95) at the rear battery when the car was started, and the alternator was charging, versus the front battery voltage of 14.18 to 14.24, I think the explanation for that is the length of the battery cable going to the rear battery.

As for the rear battery voltage dropping off before the battery message came on, I spoke to one of the Mercedes' techs and he said there is thing called the "Charge Control" in the battery circuits that tells the alternator to send all the alternator's charging voltage only to the battery circuit that has the problem, which is usually a low battery voltage reading at one of the two batteries. However, last time I had a weak battery I got a message saying, "Conveniences Unavailable"


Also, I found out this morning there is a TBS and a SB about voltage regulators needing replacement and it applied to my SL500 as well as many more models that were built in the last seven or eight years. And, on most of the treads that this was brought up on the people with the regulator problem got their regulators changed for free.


I have a Mercedes' Shop Manual (WIS) on my computer that tells how to check the alternator and regulator, but it's like reading a Greek manual. Does anyone know how to test the regulator?


As for my testing this morning, has anyone had similar problems/experiences where they were able to get the problem/s fixed and/or do you have any ideas that may be helpful?


Thanks.

 

suggesting changing the alternator regulator ic maybe faulty..

 

first call the dealer and see if the recall was ever done. that wil be free of charge. there were a couple recalls back then, crank pulley was another one. I think your car is past those recalls though.

you also have a battery control module in the trunk attached to the rear of the trunk/tail light area/spare tire area. there were software flashes for these and sometimes need replacement.

the voltages sound good that you posted. the battery in the front is mainly for starting the car. Benz calls that the starter battery, it also helps when the systems battery gets low. and the battrey in the trunk is the systems battery.

 

Took it to the dealer for repair. Turns out the alternator was bad and something called the S.A.M., whatever that is, also had to be replaced.

Thanks.