jnice72

Hello All

I have an electrical problem I am trying to sort out. Like many others, I got the "Electrical Consumers Offline" warning, which suggests the consumer battery is not above a certain voltage level and may indicate the need to change this battery (the battery is about 4 years old; I live in Florida, and the car is my weekend car, so it doesn't get driven as much as it should, and it doesn't surprise me that the consumer battery may be bad).

I recently purchased a CTEK 3300, and I hooked it to the consumer battery in the trunk. I let it charge until the full battery indicator on the CTEK was lit, and I drove it to/from work on Friday (about 22 minutes each way, with a lunchtime run of about 10 minutes each way). On the way home, I had to stop quickly, and the red "Battery Visit Workshop!" warning light came on, presumably because the braking system needed a fair jolt from the battery. Since I was only about 5 minutes away, I had no problem getting it to the driveway. When I was putting up the top in the driveway before pulling it into the garage, the red "Battery/Alternator - STOP the Car" light came on the dash. At that point, I figured at minimum the consumer battery was bad. I called MB Roadside Assistance, and they came out and changed the consumer battery ($258.61 including tax).

I drove it yesterday to the golf course and for errands, and as I was coming home in the evening the "Electrical Consumers Offline" light came briefly, then it went off. I know the consumer battery was just replaced (hopefully with a new one), so I got out the multimeter and threw it on both batteries with the car running. The starter battery was reading 14.5V, and the consumer battery was reading 11.6V.

If the starter battery was less than 14.5V, I would have said that it was probably the alternator or voltage regulator, but it is in the range I would expect with the alternator running correctly. The alternator also appears to be spinning fine, with no weird noises or smells. I am not ruling it out, but I am not ready to say definitively that it is the alternator/voltage regulator, either.

So, the $2000-3000 question is why is the consumer battery not being charged? Is it a bad BCM, relay, alternator, or voltage regulator? Anyone else ever have a similar issue? Any thoughts are appreciated before I take it to my indy.

j

seven_out

As this tech document shows, the Systems (consumer) battery is charged directly by the alternator through a 100-ampere fuse (F52f2). This suggests to me that the isolation relay and the battery control module are not a cause of the battery not charging.

Perhaps one of the alternator's diodes is bad. In this case I suppose it could be possible for the alternator to produce enough current to charge the Starter battery but not the Systems battery.

If this were my car I would probably test F52f2 even though it is probably good. Then I would test the alternator.

rune solem

I also had a problem with the rear battery, it was only getting 11.3 volt.

But after the dealer replaced a relay in the right side of the trunk, the problem was solved.

There's 2 relays, but they were cheap, so I told them to order both just in case. Didn't know for sure which was defect.

seven_out

Page 17 of the tech doc mentioned above shows the location of the two relays and describes their function.

If the Systems battery is charged, you could remove the cut-off relay (K57) from the vehicle and operation would be unaffected. The isolation relay (K75) simply powers the cigarette lighter and the power outlet located in the trunk. Therefore, I don't see how these relays could cause the problem on the original poster's car.

jnice72

Thanks for the replies. From looking at the circuit diagram in the pdf for normal operation I agree that it seems it should be the alternator; however, it seems if a diode was bad I am not sure that it would produce enough current and voltage to charge the starter battery either.

Regarding the K57 relay, which (in theory) energizes when the car goes into limp mode to draw power from the starter battery to supply essential functions, my car did go into limp mode. Here is the question: What happens if the relay sticks in the closed position? Is alternator current flowing back to the starter battery only and effectively bypassing the consumer battery/Load (i.e. consumers)? The note at the bottom of p20 of the pdf says, "N82/1 control module isolates starter battery from systems battery via open relay K57 (not energized)"

If the K57 relay is energized or stuck in closed, the two batteries are not isolated. If that is the case, replacing the relay may fix the issue. I am not sure why the alternator would not charge both batteries, then, but it evidently did not on rune solem's car. Maybe the starter battery offers the path of least resistance, especially with the relay stuck in the closed position? With the relay closed, current (in theory) does not have to go through the N82/1 module to get to the starter battery. I don't know; I am throwing $h!t against the wall at this point.

I bring this up because I spoke with an MB Service Advisor today. The first thing he said after I told him the starter battery was charging but the consumer battery was not was that a relay may be bad. I did not press further because relays are cheap, and I would just assume they start there.

Either way, I am going to have them test the alternator as well, and tonight when I get home I am going to look for loose connections at the BCM just to put my mind at ease and to see if they present themselves as laid out in the circuit diagram.

seven_out

Ohm's Law from basic electronics has to be satisfied in the circuits containing both batteries, so the Consumer battery would never be bypassed by K57.

While you are looking at your BCM you may as well check those relays with your multimeter.

jnice72

Well, the answer is both the relay and either the alternator and/or voltage regulator.

There was continuity in the relay when I pulled it off of the BCM, which suggests that it was stuck in the closed position. I got a replacement and popped it in. Unfortunately, it did not fix the consumer battery charging issue, which would suggest that the circuit diagram is correct. I brought it in for diagnosis.

During diagnosis, the STAR found an uncleared fault code for the K57 relay. The mechanic also load tested my starter battery (vintage 2007), and it failed. I had them replace the starter battery. When they hooked it up and re-ran the diagnosis, the alternator was no longer providing adequate voltage to either battery. They did not have time to run the diode test on the alternator, so I don't know if it is (hopefully) the voltage regulator or the alternator.

Here's hoping for the lesser of two evils tomorrow. It is a good thing I was an idiot and overpaid my taxes by $1900 this year. The "government savings account" will soften the blow a bit I suppose.

hhalimi

I have the exact same problem, I was wondering if the voltage regulator has solved the problem or what was the problem? I almost replaced the voltage regulator but than when I saw that the starter battery was getting 14v when the car was running and the rear was only 11.something, I held off replacing the voltage regulator.

rune solem

I had the dealer replacing the relay in the right side of the trunk.

There are 2, so since they were so cheap, they ordered both just in case.

Then the charging was ok again.

I now have about 13,7 instead of 11,3.

Nosmo SL55

I had a very similar problem. Starter battery was charging fine however the consumer battery wasn't, can't remember the exact voltages but they were similar to yours.

I replaced the voltage regulator on the alternator myself (was a ***** of a job, had to do it by feel) and no problems since.

craigndee

Hi guys, I see this is an older thread but I have a similar problem. On very cold mornings only, below 35F, when I start my 04 SL500 I am getting 2 messages. Battery convenience and ABC white message. Car starts fine. ABC works properly. I'll drive to work, only 15 minutes, park it and upon immediate restart all messages are cleared. This morning I tested with multi meter and found 14.7 volts to starter battery and 14 volts to convenience battery in trunk. Plugged in Modus computer to find several codes. ABC code C1526 Pressure supply malfunction (i believe valve not getting correct voltage at start), power supply code B1829 fuse for starter battery circuit component error, and immobilizer (alarm) B1010 voltage supply too low. I have been having an issue with my alarm system going off by itself on several occasions, including when I was driving the car. I'm assuming the alarm siren battery is bad/leaking causing the alarm issue. Since all these codes are in fact electrical related Im wondering if on very cold mornings at first start alternator not generating the right voltage? Once it warms up it works fine? Could the bad alarm battery be draining the convenience battery causing low volts at start up? Any thoughts appreciated.

itresolve

Hi,

I’ve owned MB since 2000 in 2004 I purchased an S 500 2001 and for the first year of driving I had no issues with “Consumers offline” so I purchased a replacement from MB They fitted and I continued to get the issue of consumer offline my driving hadn’t changed MB wanted £100 to test and clear any faults shown. I decided to install the original battery and put up with the charging overnight for 7-8 years. I sold the S500 and purchased an SL500 2005 same issues but I know I don’t cover more than one thousand miles a year. I ordered a consumer battery

After a couple of years, I asked MB to fit the battery again that they provided. (I did question the battery but the price to check it out was the same as buying a replacement. I was having the boot roof seal replaced and ask them to check the battery I said it was under warranty and they couldn’t at first find the purchase invoice. Anyway, they found it in the end and they confirmed the battery was faulty and replace it. Now, this where It goes a bit strange they replaced the consumer with a starter battery 75Ah.

I garage the SL500 2005 in the winter months disconnect the battery from the car and leave it from Sept to May giving it a once a month fire-up for 10-15 minutes weather permitting. I’ve just got the car back with a new MOT and had the Transmission oil replaced. (a great improvement on the gearbox). I asked them why the replacement change to a Starter Battery 75Ah when the one they replaced was 120Ah (no reply) I have Keyless entry & Keyless go also Distronic and most of the added extra’s you can purchase with the car. £97,000.00 when new. Anyway, can you help with “Why they would replace the consumer battery with the starter battery? And does it make a difference to running the consumers? Thanks in advance for any help.

jnice72

As you suggest, the consumer and starter battery are not the same. I have no idea why they would replace a 120Ah battery with a 75Ah one. The sizes and capacities aren't even close. I don't know how it would affect the performance of the consumers, but I would guess that you may not have enough current for some functions or multiple functions that require a heavier draw.

Seems weird that MB would make that mistake. When I had the initial issue, I called MB roadside service at the suggestion of this forum, and they brought out a new consumer battery and installed it for free in my driveway (only had to pay for the battery). They brought the correct battery with them.

Rudeney

There are a couple of 200amp "mega fuses" in the passenger side footwell. I'd check those:

850csi

So I have a similar problem to OP.

After a long drive home Sunday, I got the red battery symbol, which I found to be puzzling. Car seemingly worked fine until today — I was driving, AC was failing to blow cold, and I got the red “battery/alternator STOP CAR” warning.

I have the consumer battery now charging with my CTEK to see if that helps.

Multimeter readings — car off:
consumer 11.6
starter 12.5

multimeter readings — car on:
consumer about the same, stays under 12
starter 13.5

I have had some water leaking into the trunk so wouldn’t be surprised if something was up with the BCM and/or relays referenced earlier.

Any ideas?

850csi

Another data point; revving engine impacts voltage on consumer battery. Do I just have a failing battery?

thias

I think your alternator (or the voltage regulator on the alternator) is shot. Or else you would get above 14V at the rear battery with the motor running. The front battery is charged via the rear battery (using a separate regulator), that is why you still have 13.5 V there.

850csi

Yeah that's what I'm trying to figure out -- it does seem likely that it's either the alternator or the regulator, but how can I figure out which before I start replacing parts?

If the alternator was shot, wouldn't there be no difference in the rear battery with the engine running?

I do smell a funny burning smell that others have described, but I see inconsistent reports on whether that is suggestive of the alternator or the regulator.

@kbob999 do you have any input on this? I ran across your excellent DIY and troubleshooting. I don't have a STAR setup yet.

kbob999

@850csi - Good advice from others, but I'll add my 2 cents.

The RED STOP warning happens because your car is low on voltage, which could fail your SBC braking pump, which will fail your brakes. Normally you can drive 30 miles (I have) with this warning.
Low voltage means your alternator is not getting juice to the battery - which can be anything which exists between the alternator and the battery, and there is a lot in this car.

If you are getting 13-14 volts at the Rear battery with the car running at fast idle (2-3000 RPM) then your alternator is working fine.

If it is only 12 volts or so, you may have failing diodes (rectifier), or regulator, or alternator windings.
You could swap the regulator for about $40 (most common), which will give you new brushes and voltage regulating, but it may not solve the issue.
If the one or more diodes (rectifier) are bad, you may get partial voltage increase (~12 volts), but not enough amps to maintain a charge. You can buy replacement rectifiers ($80), but I would replace the alternator at this point.
If the alternator windings are bad, you will also have low or no voltage increase. New (or used) alternator required. $100-400 depending on condition.

I bought a non-OEM lifetime warranty Autozone alternator for $150. It has new everything. It failed after 500 miles and was replaced for free, but I still had to do the work.

A failed mega fuse (passenger foot well) will have no voltage increase at the rear battery when the car is running. Easy fix, difficult to check.
I'm not sure what failed battery control module symptoms are, other than your car going up in flames (not likely, but possible).
There are also battery relays in the trunk that could play a part, but rarely do.

Last - where is the smell coming from? Does it smell like burnt wiring? I would focus on parts in the area of that smell.

And finally - keep us posted on the fix so we can learn from your problem.

kbob999

This will make you smarter...

850csi

Alright, thanks for those excellent posts. The PDF is a little over my head, but I'll take another dive into it. Here's how things presented themselves today, after I drove the car a short distance. After that drive, I foolishly parked in my driveway and left my hazard lights on -- the car would not start; I had to connect my ctek to the rear battery to get the car to start so I could get it into my garage. Thereafter:

Car off:
Front battery 11.8
Rear battery 11.5

Ignition on, and a couple minutes of idling:
Front battery 11.0
Rear battery 10.7

A couple more minutes of idling, continue deteriorating:
Front 10.9
Rear 10.5

Testing at higher RPM; holding around 2500:
Front 10.5
Rear 10.1

Interestingly, when my wife would let off the gas in the last setup (so back to normal idle), the voltages actually rebounded somewhat.

Didn't detect any burning odor today.

At this point I think it's pretty clear that the batteries are not getting a charge from the alternator, and that is the most likely culprit?

Appears FCPEuro has a brand new Bosch alternator for $290.

Or could it still be the voltage regulator, if that's failed completely?

thias

The regulator (part of the alternator but you can get it separately) would be a typical part to fail. On my car it was changed twice.

850csi

Managed to get under the car and took off the alternator’s rear cover. Looks like my rectifier is fried, so I’ll be fishing out the alternator and swapping in a new one tomorrow.

850csi

So, getting the alternator out is a pretty easy job, especially if you remove the idler pulley...

But mine was stuck in very tight and could only be nudged loose with a chisel and some aggressive hammering.

Which now presents an even bigger problem — putting the new one in. Does anyone have any ideas? There appear to be some sleeves or expanding jackets of some sort that are getting in the way.




Top one especially:

850csi

So, just to close the loop, I found a couple of videos on YouTube that helped me with this idea, and it worked like an absolute charm to push those spacers out:




Bolt head -> washer -> 18mm socket (not shown) -> [onto the front side of the bracket and around the spacers] -> spacer -> nut.

Tightening the nut backed the spacer out into the socket, and it was very easy to put the new alternator in at that point.

Everything appears to be fine now.