AAG

Hi

I am getting an error Electrical Consumers Offline causing most functions to cease working (including roof operation) for about 15 minutes every time I start my SL55 AMG. I have only had the car for 2 weeks and this problem started this week. This is a 2002 car. Has anyone experienced this? Seems the second battery is not charging enough or perhaps it is analternator problem. Please let me know if you have seen this and what the soltuion turned out to be.

Thanks in advance

Walter.fr

hello AAG

I only experienced this problem, when my SL 500 was not in use for at least 4 to 6 weeks (minumum) - real problems arised when the car was parked in the garage for 4 month - then i had to visit my dealer to charge the second battery - afterwards everything was ok - cause they had to clear the memory of failures as well.

No real problem at all - you will see !!

kind regards from France

Walter

blueSL

This is standard for the SL. Everything is fine if you use the car every day, but for many owners, it's not a daily driver.

The fundamental issue is the residual battery drain when the car is not in use. After you stop using the car and lock it, various systems are shut down to conserve power but there is still a residual drain of about 200mA which will cause the battery in the trunk to lose 50% of its charge in a bit over a week. Keeping that residual current drain to a minimum must have been one of the real design headaches for the car.

The battery in the engine compartment is used to start the car and run the "must have" systems including fuel pump and engine management system as well as the starter motor and it has an almost zero residual current drain, so that battery will retain its charge over many weeks, allowing you to start the car even if the second battery is completely flat.

When you do start the car, the functions of the car which are "optional" are disabled while the battery is being charged. The issue I expect is not that there is not enough alternator capacity to run these functions and charge the battery at the same time, more that with a discharged battery, the voltage and instantaneous current sourcing ability will be reduced and heavy consumers like the roof might not work properly.

I said that the engine compartment battery provides power to start the car even if the second battery is completely flat. Unfortunately, someone forgot to note that you need to be able to get into the car in the first place. If the second battery is flat, the central locking doesn't work, nor does Keyless Go and the only way to get in is with a metal key. They couldn't put the central locking on the zero-drain battery because it has to be alive all the time "listening" for an unlock request.

This is why they dumped the Keyless Go card. You go off on holiday leaving your car at the airport, taking your Keyless Go card with you. You come back (and assuming the car has not been stolen in the meantime), the second battery is flat and you are stranded because your Keyless Go car will not unlock the car.

By dumping the keyless go card, you have to carry a real key which includes the metal key as backup. Problem solved, even if the convenience of the card alone, and especially the function which allows you to confirm (in a restaurant, say) that you really did lock the car is now denied to drivers.

One final thing to note is the Electrical Consumers Offline issue will get worse as the battery ages.

blueSL

One other thing is that if you are getting the message every time you start the car, it's likely that the battery is failing. If a lead-acid battery is allowed to go completely flat, it may never recharge properly. You bought your car second-hand and it may be the previous owner allowed it do to just that, in which case the solution is to replace the battery, but you will still get the message if you don't use the car for two or three weeks.

JackStraw

blueSL-

Do you think the rate of battery drain is higher in cars with the keyless go option than those without?

blueSL

If you have recently locked the car, the car will unlock just by touching the door handle, it will also unlock if you get the door handle wet. That says that the car is still sensing the touch on the door handle and consuming power.

Leave the car for longer though and it will not longer unlock just by touching, you have to pull the handle and you can hear a microswitch in the door handle clicking which seems to wake up the Keyless Go.

Seems to me there's an idle mode which lasts for say, an hour, during which time the car is still sensing the handle. After that, it enters a deep sleep and requires the switch to activate it.

As you would expect, the card/key consumption is very low. It is woken up when a signal is received from the car and it transmits back.

JosanK

I've had several power hungry BMW motorcycles that would drain their battereis becaue of UNGO alarms (.35 amp per day!). Solved this problem with a battery tender. The bikes accessory outlet plug would serve as input for the charger plug when the bike was off. Battery was always charged.

I've long thought that I would like to do this for the SL. Just give it a nice 1.25 amp per hour "smart" charge when sitting in the garage. Problem is hooking up the charger. No easy way to do it that I know of. I have half seriously considered getting a mod to the car by a decent electircal shop to add easy to access charging plugs for the front and rear batteries. I don't drive the car much in the winter and I worry about getting caught by a "consumer" drained battery.

Any thoughts on this?

scorchie

The battery SHOULD be removed when charging. If you don't, the car may not recognize that the battery is charged and still not start. In some extreme cases (W203 for instance), charging the battery in the car can cause permanent damage to the car's electronics.

"winter" ... in San Jose, CA? Ummmmmm...

-s-

AAG

Thanks for your reply.... Once I get the chance I will take the car in and find out what they say and let you know. I live in the South of France and everyone is telling me how bad MB service shops are so I am dreading going in.

blueSL

I agree the battery should be disconnected from the car, but it's a moot point whether it needs to be actually removed, especially if you charge it in open air with the trunk lid open, important to use a smart battery charger which doesn't go on piling in the amps.

That said, I'm pretty sure my battery is now shot, it will not hold its charge and it will never get to the stage of "fully charged" on my battery charger. Too many times I've let it go flat when I haven't used the car for a few weeks, I guess.

I'll get the dealer to change it when I take it in for the SBC safety recall.

JosanK

A question: If you slowly charged a battery, which was not fully discharged, with a slow "smart" charger as a preventitive maintenance move would there be a problem? Even if the car is drawing some power for things like the keyless go receiver a 1.25 amp per hour charge seems pretty delicate. This would be maybe a once a week procedure if you're not driving the car.

Would this upset the SL55 electronics?

Charging a totally dead battery is a different issue. The idea is to not let it go dead.

mattnaz

I just leave a trickle charger on the battery when I know the car will be sitting for a long period of time. I have never had a problem with the SL after sitting for 3 weeks. Everything is fine as long as I don't lock the doors.

blueSL

I think you're correct. Battery chargers can range from a very crude high capacity transformer to a smart charger which will regulate the current to charge the battery correctly, and if all you want to do is to trickle charge the battery, a resistor in series will do the job. You only need to get cleverer if you wish to charge the battery at high currents.

I think a 12v transformer (which will generate more than that off load), through a bridge rectifier and a 10 ohm 10 W current limiting resistor will be just fine.

My own smart charger was charging the battery today at between 7 and 3.4 A and never got to the stage where it thought the battery was fully charged. The battery is rated at 70 AH (contrast with my SL600 which has 100 AH but this has to do everything), so it should have fully charged in a day. It's that which makes me think the battery is shot. For now, there's no "consumers offline" message, but tomorrow will probably be a different story.

Normally, I wouldn't go to the dealer for a new battery but it looks like this one has a non-standard mounting flange which means you have to buy Mercedes instead of after-market.

Certainly agree that you should not let a battery go completely flat. If you do, they need coaxing to come back to life with very low initial recharge and you only need one of the 6 cells making up the battery to go bad to spoil your day.

AAG

Turns out a cable that controls the lock on the glove compartment was leaking power causing a drain on the battery. A new cable and a new battery later and it seems the problem is solved.

Regards