mbdreamr

My CLS55 started displaying the red battery light then would shut off all convenience features. It then displayed low braking power and ABS, BAS, ESP lights came on.

I checked the battery voltages and they seemed fine. When I checked the charging it was low so I decided to replace the voltage regulator on the back of the alternator.

I started the car up drove for about a mile and what do you know the damn red battery light came on again. I checked the batteries they were good, and charging seems fine too. On the dash it shows that it is steady at 14-14.1 at idle. However, when I drive I see a dip in the charging going down to the 12s then back up.

I realized that the light will only come on after going past 3k RPM the convenience features will shut off. But the tricky part is that the light will go away and the features will start working if I keep it under 3k RPM.

I tried looking for any posts about this and they were all over the place including the battery control module.

Please help me out fellow members.

machild

You are going to need to have it scanned using MB Star/SDS to see what is going on. Find a good MB independent shop and have them hook up the car and see what is going on with the charging system.

mbdreamr

Thanks Machlid that was the next step. Kind of annoying that I can’t drive her. But it’s ok, have to figure out what’s wrong.

A shame that at 67k having these issues.

machild

Could be the Battery Control Module is failing. Plenty of those available from salvage yards for easy money. Make sure you report back what you find out so we can all benefit from it. Good luck.

mbdreamr

Just ran a diagnostic on the car and the BCM isn’t throwing any codes. There was a lot of stored codes when the voltage had dropped previous to the Voltage Regulator change.

However, one more thing at play here is the Voltage Regulator is an aftermarket one. I wanted to put the OE Bosch one but had to order at dealership. My local part supplier only had aftermarket.

I may order from stealership and put OE to see if that’s it.

machild

Bosch rgulater could be an issue. When you get one make sure it has the same Bosch number on it as what you had originally. If you get it from MB then it sould be the correct part. There are lots of differnt regulators and I don't know if Bosch sell a more generic version in the open aftermarket and whether it is correct for your car. But, going with the Bosch unit is a step in the right direction. No chance your serpentine belt is slipping especially over 3,000 rpm?

mbdreamr

Haven’t checked the belt. It was replaced before I bought the car back in November 2019. Be a good idea to check that too. Slim chance it could be it.

I ended up just buying a new Bosch Alternator. Don’t want to risk changing the voltage regulator to end up finding out I’ll need the alternator.

what gets me is that the charging seems fine at idle and when the car is cold it does it closer to 3k RPM. when the car warms up then it starts to do it at lower RPMs.

hopefully it’ll be sorted out soon. I’ll keep you posted.

C32owner

I would say its your alternator. Have a look at the back of it and see if any caps have burnt off.

mbdreamr

Nothing burnt off as mentioned I went ahead and purchased a Bosch alternator and am just going to replace it. Nothing else seems to be giving a code. Alternator must be shot for the voltage to fluctuate when giving load.

mbdreamr

Update:

I just changed the alternator today and the problem is resolved. It was the alternator after all.

Thank you for the responses.

machild

Glad yoiu got it sorted out.

C32owner

Awesome, congrats on getting it fixed. Always nice to have problems solved. Enjoy

mbdreamr

Thanks guys. I’m very happy it’s sorted out finally. I’ve been enjoying her for the last few days.

Usually I drive her about once a week. Use the Prius for commuting lol.

C32owner

Lol thought I was bad, with a mini as a daily then jumping in the cls for the blast lol..

mbdreamr

😂 I used to have a 12 Mini Cooper clubman S stickshift. It was a blast to drive. But the Prius gives great gas mileage and then when I drive the CLS I appreciate the power difference.

lol have to balance my gas mileage CLS is horrible and my Prius I average 48-50.