SLK Indicator lights staying on - Possible fix - Mercedes-Benz Forum
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post #1 of 39 (permalink) Old 01-05-2008, 11:43 AM Thread Starter
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SLK Indicator lights staying on - Possible fix

1999 SLK 230 (RHD UK car )

Hi All

I searched this forum to help me fix the indicators which were staying on on.
Got lots of help and was able to eventually sort out a fix which may be useful to other folks.

The fault was in the mulitfunction relay unit - part num 170-820-09-26. (This is a plus £500 unit to replace).
I managed to fix the fault without needing to buy a new one.
One of the relays was sticking due to pitting caused by general wear. A rub with some emery paper got it freed up.

Here is a guide for anyone else facing this. some pics are attached.

The relay is in the big relay box under the bonnet next to the battery. (It looks like it may be a filter unit for the aircon)
Lid on the box has 4 screws holding it on.
The relay unit in question is the one next to the battery (on RHD car)

Now - Remove the plug nearest to the front of the car - you will need to unlock it by sliding the grey toward the front of the car.

There is a metal handle thing at this end of the unit, pull it upwards and it will release the rest of the plugs.

With a bit of wiggling you can now remove the unit from the box.

Unscrew the 5 star screws holding the lid on.
You will see 3 gold coloured relays , the one that flashers the indicators is the one furthest away from the edge of the box. (If you hold the unit with the connnectors at the top, it is the one on the far right.

On mine this relay was sticking when closed.
I used a bit of folded emery paper to clean the contacts which stopped it sticking.

And in true workshop manual speak - reassembly is a reversal of the above.

This may not work for all faults with these units, but it is worth a try.

Cheers
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post #2 of 39 (permalink) Old 01-05-2008, 08:00 PM
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You did well to get the CCM unit out completely. I tried but was always afraid I would break that big connector.
It's also a good idea to disconnect the battery negative first. These modules don't take kindly to being partly disconnected with power on.


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post #3 of 39 (permalink) Old 01-06-2008, 06:56 AM Thread Starter
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Thanks for pointing out about disconnecting battery, you can see it disconnected in the pics.
Had too many surprises in the past to take chances.

Cheers
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post #4 of 39 (permalink) Old 01-06-2008, 01:56 PM
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Sorry, didn't notice the pic - indeed it was disconnected.
Surge arrestor (see other posts) is a good idea too. It stays connected to the second threaded post on the negative battery cable. Don't see one on the pic. :-)


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post #5 of 39 (permalink) Old 01-07-2008, 06:59 AM
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Thanks for the info. Mine won't flash every once in a while then starts working again, I will give this a try.

Avery
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post #6 of 39 (permalink) Old 01-18-2009, 06:47 AM
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Thanks for the pics, I need to try this as mine went last night.

Nig
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post #7 of 39 (permalink) Old 01-18-2009, 08:30 AM
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ya this module is about 700$ from the cheapest place i found so it is worth investigating! Is it possible to replace that relay on the board? anyone have a source for the relay?
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post #8 of 39 (permalink) Old 02-04-2009, 05:31 AM
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Thanks very much for this Chris.

I had actually done this and had closed up the module before I found this thread. I had given all the relays a bit of a clean but I was actually looking for a dry joint (none found). After reading your suggestions I opened it up again and gave that relay a good clean-up. So far so good.

One question - how did you know that this relay is the flasher?
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post #9 of 39 (permalink) Old 02-08-2009, 10:53 AM
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Hi Chris,

I'm also in the UK and a member of the Merecedes-Benz Club.

I've repaired the CCM/Multifunction module on my 1996 SLK and two others (1998 cars) as well. The permanent fix was to change the defective relay. I managed to source a replacement relay but had to buy a minimum order quantity so I do have some spare relays for sale.

Changing the relay is a two person job as you need an SMD workstation to heat the relay frame (person 1) with the hot air gun while person 2 heats the relay pins on the reverse side of the circuit board with a 80W to 100W wide tipped soldering iron. Person 1 slowly pulls the relay free with a samll pair of pliers. You then you need a vacuum powered desoldering tool to remove the solder from the holes in the circuit board. I have attached some pics of the worn out relay contacts from my CCM module.

For others reading this post I am willing to replace relays in these modules for a reasonable price plus shipping. If it's something that I can help you with then by all means send me a PM.
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post #10 of 39 (permalink) Old 02-09-2009, 09:09 AM
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Nice job tracing the fault down to the specific relay. We have had this fault intermittently for the last few years. I will definitely clean that relay up when I get a "round tuit". Looks like it could use an arc-suppression diode pair across the contacts.
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