Hello all,
Picked up a 2003 SL55 in the spring and have found this site to be a ton of help so far. Here is one I haven't been able to nail down after plenty of searching on the topic.

After sitting for 2 or 3 weeks, I went to start the car and got the white consumer battery offline message. Drove for a bit and it disappeared. Then when I went to start the car again a couple of days later, I got the red workshop warning, and it won't go away. Using my icarsoft reader the fault code is B1828 K57 (battery disconnection relay), accompanied *sometimes* with the B1832 G1/4 historic component (start fault battery).

I removed the K57 relay and it tested fine. I went ahead and replaced it anyway because it's cheap and only a minor pain to get to, but the fault code remains.

A few things:
Both starter and consumer battery were replaced less than a year ago.
Real-time charging is over 14V with engine running. The alternator was replaced back in 2005 according to the service records, and a recent test at Advance Auto passed the battery and alternator FWIW...although I don't put much faith in that.
No dimming of exterior/interior lights ever.
Have removed the rear battery from the car and charged it to full over a few days, code still there after reconnecting.
Disconnected both rear and front batteries (in the correct order) for the heck of it. No change.

The car drives fine and both batteries take a charge after driving. But are the drops below indicative of a parasitic draw? Even if so, I've had both batteries on tenders after charging and the code is still there.
Starter battery:
12.16 car off, cold
14.04 car running
13.0 after 30 mins or so of driving
Day later, cold, back to 12.20

Rear consumer battery:
12.14 car off
14.10 running
12.87 after 30 mins or so of driving
Day later, cold, back to 12.22

I just can't imagine one or both of these batteries are bad after less than a year, and it appears the alternator and voltage regulator are doing their job if I'm seeing over 14v while running. I've read about a fuse under the passenger footwell that is of course a pain to get to that may have blown, but wouldn't this point to the starter battery not getting a charge? I haven't pulled just the starter battery and charged overnight, I could try that. What is left? A bad battery control module? Just drive and ignore forever since the car runs fine??

 

I don't have the software. Is that the only route to take here?

 

Did you ever fix the k57 battery disconnection relay fault?

 

Funny you should ask. It literally just randomly stopped popping up the last few times I’ve started the car over the last couple of weeks.

I keep the rear battery on a tender if I don’t drive it for about a week or so, but this recent disappearance of the red warning light didn’t happen while it was on the tender; I’ve just been driving it a bit more than usual.

The only change I ever made was replacing the relay in the trunk. The original relay actually tested fine, but I went ahead and replaced it in an attempt to cheaply fix the problem.

I’ve just kept an eye on the levels of both batteries (after removing them and fully charging outside of the car), and the alternator seems to be doing its job.

I just ignored the light and will do so again if it pops up.

 

hmm strange one, see i have had red light for ages now and its so annoying but i have heard apparently having the red light is a battery system malfunction and it can cause minor problems like not having the braking sbc working to it full ability etc apparently it restricts power to certain modules to preserve battery life etc etc so it got me thinking

 

Not sure. I think it’s the BCM, battery control module, in the trunk, but they’re like $800 for a used one on eBay and that’s an expensive guess. Don’t want to just throw money at it if I’m not 100% sure if that is the fix.

I’m just monitoring both batteries to ensure they’re charged and leaving it on a tender when not driving.

 

fair enough and is your only code the k57?
I thought it bcm was faulty a different code would show saying faulty bcm etc? Unless the k57 is a problem with the bcm

 

I read on here that it could be the BCM, and also had a MB mechanic say that’s what he thought it was. I’m sure there are other codes that specify a truly faulty BCM, but also I would figure there would be more serious issues. In my case, all functions work and both batteries are charging properly.

My code was B1828 K57 (battery disconnection relay), accompanied *sometimes* with the B1832 G1/4 historic component (start fault battery).