1998 SLK230 104k miles, no major problems. Last night the engine light was on. Going down the interstate the the car shut off power the radio, and the brake and ASR lights came on, then the lights went dim and I stuttered into a gas station... I got a jump for a couple minutes, and it started and I made it to the next gas station, then a friend came and we charged the battery for 15 min, and I made it to my destination.. stayed over and brought the car home in the morning, it started on it's own, but having to jump it halfway home... I brought it home and fully charged the battery...

I put a meter on the Alternator lead that goes to the little black box with part number 002 542 20 19 (google returns "RELAY BATTERY CUT-OFF") and the ALternator is putting out 19.5V, but it is not going throught the box to the terminal that goes to the battery.

Anyone have a wiring digram to tell me what the three leads are going into the control portion of this box so I can test?



possible (probable) cause:
I washed the engine compartment (hose and soapy water, not pressure washed) last week becaue my friends were giving me a hard time about how dirty it was... the connector to the relay was dry inside, and the computer is sealed... the right blinker went out at about the same time... really funky...


Thanks,
Michael Cotherman
Clearwater, FL

Your alternator is putting out 19.5V? That should be more like 14.5V. Did you get your alternator wet. You could have fried the regulator inside.

How old is your battery? You could have a week cell or an open circuit inside it that is not letting it hold a charge. If your battery has problem too that could cause your alternator output to be too high.

You may have heard about people making the mistake of disconnecting the battery while the engine is running as a test to see if the car dies. This is a BAD thing to do for the cars electrical system. The regulator cranks up to full when it sees the open circuit and overloads everything.

I would try a new battery first.

the 19.5 V is because it is open circuit, no load on the alternator...

I did a little more testing of the battery cut-out relay, and there is voltage (12V) between the brown(ground) and the black w/ red stripe wire when the ignition is on but the relay does not pass the voltage to the battery.

If I manually connect the contacts of the relay, connecting th Alternator output to the battery, it charges the Battery and is at 13.5V... I am 99.9% sure it is the battery cutout relay now, but still want to see what the other wire, Green w. Black stripe does...



-mike

Same thing happened to me yesterday. I got a new battery and the same thing happened again. except i made it home before it started to stutter. I tested the battery and it has 11.4V when the engine was off and 9.2V when the car was turned on idle. I think i'm having problems with my alternator. Does anyone know for sure way to test if it is really the alternator or not. Is it difficult changing the alternator, or should i just take it to the dealer.

Thank Mike

Mike, If I were you, I would have the alternator tested. Places like Autozone might be able to at least test it even though they may not be able to get you the part. It is not that hard to change yourself but it is in a tight space. It is trouble if the new alternator has a different pully on it and you have to swap it with the original one. Also make sure the battery is disconnected when you disconect and reconnect the wires to the alternator. A visit to the dealership might cost you $300 for parts and labor. You should be able to get one online cheaper and then save on the labor by installing it yourself if you feel up to it.

Sorry, and do not want to flame anyone...

The alternator is fine... I stated taht initially. Alternators will put out a very high voltage if their is NO load on them, I guarantee if you undo your alternator lead, you will get more than 14 volts.. that is the way electricity works, I am an electrical engineer, I was just asking for the wiring diagrams or actual experience with the system...

I spoke to an actual friend of a friend who is a mechanic, and the battery cut-out relay is a known problem, I replaced it for $50 and it has worked fine since...

-Mike

Mike( or anyone);
I had the exact same problem and got all excited when I read the simple solution but when I replaced the relay, nothing changed. Does anyone know of a reason that a new K56 battery cut-off relay would fail to pass the charge on to the battery? Where does the signal come from that activates the relay? I presume the signal to turn the relay on or off comes from the plug on the rhs, but where does that plug get its signal?
Ernie

PS I never had a warning lamp come on, even when there was no battery charging andthe voltage was low.

All greetings. I too solve this problem. Contact piece Kl.15 it +12V at the engaged ignition, Kl.31 is ground, AS is the control package trigger airbag. In WIS there is a document in which the algorithm of work K56 is specified. At operation airbag, there is a breakage of one of two fuse, in a consequence of that there is a switching-off ê56. Only it is completely not clear, what safety locks mean. Probably they in most ê56 are located, or in other place.
Sorry for my English

i have the same problem with my SLK. My battery looses power after driving my car for about 1 hour. But if I drive it for less than an hour, It seems that its charging because all lights,windows,horn are working well.

I will know when the battery is drained because of the ASR and SRS light will turn on and eventually turn of my car due to a Dead battery.

At first I thought that the battery was faulting. But it still did the same with my Brand NEw battery.

Can anyone shed light on this matter as to how can i fix this problem? I don't understand what a k56 relay means ( based from the replies above )?

There is a heavy duty relay in front of the battery. It disconnects the battery from the alternator when the car is shut off. Test it, if it is not working, replace it.
I found the below pic in a few seconds with Google:

i'm so sorry for the ignorance regarding this. I'm not so familiar with electrical parts. How can I test it? and what are the parameters and signs to know if its working or not? thank you

Same thing happened to me also, my mechanic friend open up the K56 relay and looked at the little computer board inside, he turn it over and spot welding solder, all the little contact metal nipples, After that every thing worked great!
But it took awhile for him to open the relay box, he had to use a small screw drive, and keep scrapping between the gap of the relay box top, then the top of the relay final came off, to view the inside.

Same thing happened to me also, my mechanic friend open up the K56 relay and looked at the little computer board inside, he turn it over and spot welding solder, all the little contact metal nipples, After that every thing worked great!
But it took awhile for him to open the relay box, he had to use a small screw drive, and keep scrapping between the gap of the relay box top, then the top of the relay final came off, to view the inside.