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Battery Low Conv. features limited...Not sure next step.

1K views 15 replies 10 participants last post by  Mike NZ 
#1 ·
Been lurking on this forum for about a year. I have a E500 and I have the much asked about Red Battery Alert that shows up on the dash.

I have seen several people say its the Aux (secondary) battery in the front of the car. Replaced it. Problem continues.

I have seen people say no no no its the rear battery. It tests 98% and the Alternator/VR is new (replaced 3 months ago) and tests out fine.

Could it be my belts?

I notice the problems only happens after I have driven the car in this Texas 100+ heat for over an hour or so with the A/C on fully, the radio on and nav system on and lights.

When the light comes on and I turn off some of the electronics...i can safely run the A/C at 50% without any issues.

Other times when I have the problem. After the vehicle has been in an outside lot.

Today the car thermometer read 113 when I got in it and on a previous occasion 116...both time the light came on but as I drove to highway speed and the temp came down. The light went off and I could run the A/C no problem.

Could this be a belt issue...? Hate to go in and have it be a fishing expedition at the Dealership.
 
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#2 ·
Someone mentioned the brake light switch being the culprit. I bought an OEM version from Amazon for $15 IIRC and I will get it installed. I know I need to swap the Aux battery...but it's a cheap first step. I was just about the rebuild my Alt.
 
#3 ·
jhawkin972,

I was in your shoes, almost . My front small auxilary battery had been changed several months before. Then the same alert you described began to appear on my dash at start ups . Mine happened regularly if I didn't drive the car for a few days. Once the car was started and running for less than a minute , it would disappear. So I had the main battery in the back tested and it turned out to be the original battery. My car is an 04 model year E320. I would have the system checked to see if the alternator is putting out what it's supposed to and then if it is, look to the rear main battery for it's condition....

Good luck ! Get it done quickly. It's too hot for this nonsense....
 
#4 ·
I have had that issue and it is/was a parasitic draw just about one amp. Took a few days to drain the battery enough and it wouldn't start the car. But if it did start but was low then the alert came on. I had to start to pull fuses to find the issue- and I still have it from time to time in my w211.
 
#7 · (Edited)
http://www.benzworld.org/forums/w21...entification-parasitic-draw.html#post12179681
Now, later in the summer I get both warnings- SRS and Tele-aid (IIRC). With all fuses back installed. I clear both warnings with the steering wheel button and haven't had the draw drain the battery lately- but I don't know if the airbags are working as designed. I'm afraid to go to the dealer here on Long Island for fear they will charge me a thousand bucks for doing almost nothing. My center computer screen also does not work; and no stereo either. Otherwise car drives perfectly and I don't listed to the stereo normally anyways.
 
#6 ·
Jhawkins972,

I suppose the belt and tensioner could play a role in your situation.
Any idea how old either is?
On my 98 E320, I found that the tensioner was weak. I used to have a light burning rubber odor following a long ride, more than one hour, with a lot of consumers running.
Decided that the tensioner was suspect. Before I removed the old one I put a beam torque wrench on the release bolt and measured the tension that would move the tensioner away from the belt.
Result was +-25 ft lbs.
New one was 50+ to do the same.
No more odor with the new one under the same conditions.

Skippy
 
#8 ·
The belt is about 2 years old. The rear battery is about 3 years old and I just had the alt. vr put on about 4 months ago at a local shop....perhaps they didnt set the tension correctly. Having that check today. If that doesn't fix the problem off to see bonnie and clyde at the dealership tomorrow. I am hoping its the belt slipping when hot or stressed. Hate the guessing game at the dealership.
 
#9 ·
The tension on the belt is applied via the self tensioner, its not adjustable, there are 2 marks on the tensioner housing, the shaft mark needs to be in-between these 2 marks while the engine is running, it also needs to be stable without too much jumping.
Normally when the tensioner goes, the belt starts misaligning and fraying.
 
#12 ·
OK Broke Down and Got a New Rear Battery

And it didn't fix the problem. So I have a new alternator, new main battery, and new aux battery. But still the problem.

CVincent I think mention wiring. I said in my first post that the problem seem heat related, and intermittent. The car would run fine if I lowered the A/C and turned a few things off.

So I asked this afternoon about grounding issues after reading this -

Good grounds are important because poor grounds cause voltage drop. The consequence of this voltage drop is that the systems in that circuit can malfunction. How do bad grounds cause voltage drop? Well, the answer is Ohms Law.
Ohm's Law states that V=IR. This means that the voltage drop (V) is proportional to the current through the circuit (I) and the resistance (R) of the resistor (or bad ground in our case). An easy example is attempting to draw 10 amps through a bad ground with a resistance of 1 Ohm. So V=10(1) thus making the voltage drop a whopping 10V. This leaves only 2 volts available (in a standard automotive 12V system) to power the circuit and means that all that extra power must be dissipated as heat at the resistor (bad ground). Generally this heat makes the condition even worse, causing more voltage drop and more heat. In the most severe cases the ground will function under light loads yet fail under high current draws causing what appears to be an intermittent failure. Many people have seen this behavior caused by a loose (high resistance) battery terminal


Im guess I will have a mech. look at the wiring system between the charging components and the SBC unit that was replaced by the dealership a few weeks prior....just to make sure its grounded correctly.
 
#15 ·
i could believe the bmc would malfunction when it gets hot, mine only came on once but i was close to the dealer so took it right in for diagnosis

dealer told me that i could drive it for the next few days while we waited for the part but i parked it to be safe

think if it is starting and running ok you are probably fine until next week...

mine was not switching over and charging the aux battery anymore i guess


there is an update for the bmc , mercedes has a bulletin of some sort about this, not sure if we have to pay for that update or not
mine would not communicate at all with the star so had to be replaced

you can find them online for about 500, maybe a little less

but it has to be programmed with a star machine anyway

good luck, let us know what you find out
 
#16 ·
Just for the record, my problems all disappeared when I replaced both batteries with Mercedes Benz batteries.
Yes, they were expensive, particularly the rear battery, but to me it was money well spent.
 
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