Alright so I have a laundry list of things that have been replaced some by me and some by old owner. I got the car with 78k on it and have had battery problems ever since. I will wake up and get in the car in the morning and the red battery light comes on and I have no convenience features. After I drive 10 min and shut the car off for fuel or groceries, all functions are restored and I'm good for the day no matter how many times I shut the car down. If it sits for more than 6 hours ish? The warning comes back. If I drive the car with the warning for 45 mins though I will still not have any convenience functions the entire time.

I have combed through all the battery sections of all the forums (I think) and I dont know what to replace next if anything. Im sure I missed something but I dont know where. Below is what has been replaced. Any help appreciated. I'm not new to forums but I am new to posting in one so be gentle .

New interstate rear battery 67k (3 years ago)

New alternator 68k

Replaced auxiliary battery relay and fuse 68k

Replaced battery control module 68k

New alternator and regulator 70k

New interstate rear battery 76k (1 year ago)

New alternator regulator 80k

New interstate front battery 81k (yesterday)

Battery codes cleared and BCM reset 81k

Rear Interstate battery tested passed with flying colors 81k (yesterday)

 

Since clearing the battery codes at 81k miles what codes have come back? That will help to understand what faults are currently occuring and possilby what is causing your issue(s).

 

well to be honest I dont fully understand the BCM unit. There are no engine codes. and no codes I can see other than the red battery light and the convenience function off message. I was told by a shop I took it to that there were error messages in the BCM that were cleared because the BCM thought there was a bad battery still when there wasn't. I haven't had the BCM reset since and that was 2 weeks ago.

 

Engine code readers will not show you all the other contollers on the car - and there are a bunch, maybe up to 25 of them. The BCM is jsut one of them but you need to query all of the others to see what is going on. Each controller is essentially a stand alone simple computer with all of them networked together throughout the car. You will need a much more robust diagnostic tool than a simple engine code reader. The MB Star system is the best and will help to point you in the direction of what is going on with the car. Find a shop that has Star and have them help you fingure out what is going on with the batteries. Good luck.

 

What's the battery drain in amps when the car is locked?

 

I took it to a shop today and they said that it was drawing 250 milliamperes when locked and they said thats way too much. It turns out it was the telephone tracking system that was drawing the energy so they disabled it and coded it out. Now they say its drawing 89-95 milliamperes while locked and they said anything under 100 is perfect. The mechanic thinks it was getting drained below a threshold overnight and then recharging on the first drive. Does that sound right?

 

200mA is definitely too high yeah. 100mA is still a bit on the higher side, but it could be margin of error while measuring. If the battery error doesn't come anymore, I guess that was the cause.

 

New alternator again last week.

Replaced the SAM module and no dice.

Unplugged the K57 relay and nothing changed.

Unplugged the K75 relay nothing changed.

Can someone please help?

 

So the issue seems to be the SAM unit is not seeing the alternator charging for whatever reason. but the separate engine management system is seeing charging. thats why it always starts and the batteries are always charged. But I've been through 4 OEM Bosch alternator and and control modules and nothing works. There is a communication error between the SAM and the alternator but replacing the SAM with a newer one did nothing.

Ideas?

 

The draw was high and it was the telephone stuff so they disabled it and we are siting at below 80 milliamperes when the car is off which is normal. The batteries are always charged so that isn't the issue. It seems to be the communication from the SAM to the alternator. At least thats my guess and my MD techs guess too.

 

Why was the Sam and alternator changed?
What is the battery draw currently when the car is locked?

 

currently when locked it draws between 80-90 milliamperes which I'm told is perfect. There is always plenty of juice in the batteries so that isn't the problem. SAM and alternator were changed because the error code is the SAM is not seeing the charging alternator even though it is charging normal. I dont have the exact codes (this is all done at a MB shop and that is what his $30k MB scanner tool is telling us.

 

Can you post the xentry short test here with all error codes?

 

Alrighty, after 3 weeks at the shop hours of wire tracing and making sure all the clips were in good shape the alternator was sending the correct voltage to the BCM. But, the BCM was reading 3v in the diagnostic tool. So, after swiping the BCM again and trouble shooting my guy did a diag of the SAM module in the front of the car. Turns out the version was 1.91 or something along those lines and it needed to be updated to 2.11. Then after that it would see the circuit fault on circuit 61 or 62 (can't remember but it is one of those) and ask if you wanted to reset/clear those fault lines and the battery light is now gone finally! We didn't think that was the case because we swapped the SAM out with a newer SAM to cross that off the list. Turns out both needed to be updated. I hope this helps anyone with a persistent battery light even if you change every battery related component like me.

 

Wow. Well, this is where Benzninja's service would have paid dividends.

Also makes me wonder what the cause of the original fault was. I guess you had the drain which was causing the light originally. Then you fixed the drain, and you were unable to reset the light until you updated the SAM.